Commit Graph

378 Commits

Author SHA1 Message Date
John Ericson e0eeae9a44 [lld][clang][cmake] Clean up a few things
- If not using `llvm-config`, `LLVM_MAIN_SRC_DIR` now has a sane default

- `LLVM_CONFIG_PATH` will continue to work for LLD for back compat.

- More quoting of paths in an abundance of caution.

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D118792
2022-02-03 20:01:28 +00:00
Qiu Chaofan b797d5e6b2 [CMake] [Clang] Add option to specify PowerPC long double format
This method introduces new CMake variable
PPC_LINUX_DEFAULT_IEEELONGDOUBLE (false by default) to enable fp128 as
default long double format.

Reviewed By: jsji

Differential Revision: https://reviews.llvm.org/D118110
2022-01-27 00:50:53 +08:00
John Ericson 10d0d8c0c1 [clang][cmake] Use `GNUInstallDirs` to support custom installation dirs
I am breaking apart D99484 so the cause of build failures is easier to
understand.

Differential Revision: https://reviews.llvm.org/D117419
2022-01-21 23:58:08 +00:00
John Ericson da77db58d7 Revert "[cmake] Use `GNUInstallDirs` to support custom installation dirs."
https://lab.llvm.org/buildbot/#/builders/46/builds/21146 Still have
this odd error, not sure how to reproduce, so I will just try breaking
up my patch.

This reverts commit 4a678f8072.
2022-01-16 05:48:30 +00:00
John Ericson 4a678f8072 [cmake] Use `GNUInstallDirs` to support custom installation dirs.
This is the original patch in my GNUInstallDirs series, now last to merge as the final piece!

It arose as a new draft of D28234. I initially did the unorthodox thing of pushing to that when I wasn't the original author, but since I ended up

 - Using `GNUInstallDirs`, rather than mimicking it, as the original author was hesitant to do but others requested.

 - Converting all the packages, not just LLVM, effecting many more projects than LLVM itself.

I figured it was time to make a new revision.

I have used this patch series (and many back-ports) as the basis of https://github.com/NixOS/nixpkgs/pull/111487 for my distro (NixOS), which was merged last spring (2021). It looked like people were generally on board in D28234, but I make note of this here in case extra motivation is useful.

---

As pointed out in the original issue, a central tension is that LLVM already has some partial support for these sorts of things. Variables like `COMPILER_RT_INSTALL_PATH` have already been dealt with. Variables like `LLVM_LIBDIR_SUFFIX` however, will require further work, so that we may use `CMAKE_INSTALL_LIBDIR`.

These remaining items will be addressed in further patches. What is here is now rote and so we should get it out of the way before dealing more intricately with the remainder.

Reviewed By: #libunwind, #libc, #libc_abi, compnerd

Differential Revision: https://reviews.llvm.org/D99484
2022-01-16 05:33:07 +00:00
John Ericson 6e52bfe09d Revert "[cmake] Use `GNUInstallDirs` to support custom installation dirs."
Sorry for the disruption, I will try again later.

This reverts commit efeb501970.
2022-01-15 07:35:02 +00:00
John Ericson efeb501970 [cmake] Use `GNUInstallDirs` to support custom installation dirs.
This is the original patch in my GNUInstallDirs series, now last to merge as the final piece!

It arose as a new draft of D28234. I initially did the unorthodox thing of pushing to that when I wasn't the original author, but since I ended up

 - Using `GNUInstallDirs`, rather than mimicking it, as the original author was hesitant to do but others requested.

 - Converting all the packages, not just LLVM, effecting many more projects than LLVM itself.

I figured it was time to make a new revision.

I have used this patch series (and many back-ports) as the basis of https://github.com/NixOS/nixpkgs/pull/111487 for my distro (NixOS), which was merged last spring (2021). It looked like people were generally on board in D28234, but I make note of this here in case extra motivation is useful.

---

As pointed out in the original issue, a central tension is that LLVM already has some partial support for these sorts of things. Variables like `COMPILER_RT_INSTALL_PATH` have already been dealt with. Variables like `LLVM_LIBDIR_SUFFIX` however, will require further work, so that we may use `CMAKE_INSTALL_LIBDIR`.

These remaining items will be addressed in further patches. What is here is now rote and so we should get it out of the way before dealing more intricately with the remainder.

Reviewed By: #libunwind, #libc, #libc_abi, compnerd

Differential Revision: https://reviews.llvm.org/D99484
2022-01-15 01:08:35 +00:00
John Ericson 44e3365775 [CMake] Factor out config prefix finding logic
See the docs in the new function for details.

 I think I found every instance of this copy pasted code. Polly could
 also use it, but currently does something different, so I will save the
 behavior change for a future revision.

We get the shared, non-installed CMake modules following the pattern
established in D116472.

It might be good to have LLD and Flang also use this, but that would be
a functional change and so I leave it as future work.

Reviewed By: beanz, lebedev.ri

Differential Revision: https://reviews.llvm.org/D116521
2022-01-07 20:16:18 +00:00
John Ericson a3ab2c94a2 [clang][cmake] Rearrange top-level CMakeLists.txt for D116492
In that revision, I make LLD match Clang in deprecating `llvm-config`.
This patch isn't to worthwhile on its own --- there isn't a sense in
which the new order is "better" in isolation --- but by putting the
steps that LLD also neeeds to do first, I make the diff between LLD and
Clang's top-level `CMakeLists.txt` very legible.

Longer term I hope:

 1. We can remove calling `llvm-config` altogether, and just go strait to
    finding the CMake config file. This is what Flang does, at least.

 2. Hopefully the diffable part is smaller then --- i.e. there is less
    duplicated boilerplate.

 3. Any duplicate boilerplate that remains can be factored out.

I didn't both trying to factor anything out in e.g. the top level common
CMake Utility modules because this deprecated-but-not-removed state is a
merely transitional.

Reviewed By: beanz

Differential Revision: https://reviews.llvm.org/D116548
2022-01-03 18:28:34 +00:00
Fangrui Song b5d3bbcc94 [CMake] Remove unneeded CLANG_DEFAULT_PIE_ON_LINUX canonicalization after D115751 2021-12-28 10:49:52 -08:00
Fangrui Song 1042de9058 [Driver] Add CLANG_DEFAULT_PIE_ON_LINUX to emulate GCC --enable-default-pie
In 2015-05, GCC added the configure option `--enable-default-pie`. When enabled,

* in the absence of -fno-pic/-fpie/-fpic (and their upper-case variants), -fPIE is the default.
* in the absence of -no-pie/-pie/-shared/-static/-static-pie, -pie is the default.

This has been adopted by all(?) major distros.

I think default PIE is the majority in the Linux world, but
--disable-default-pie users is not that uncommon because GCC upstream hasn't
switched the default yet (https://gcc.gnu.org/PR103398).

This patch add CLANG_DEFAULT_PIE_ON_LINUX which allows distros to use default PIE.
The option is justified as its adoption can be very high among Linux distros
to make Clang default match GCC, and is likely a future-new-default, at which
point we will remove CLANG_DEFAULT_PIE_ON_LINUX.
The lit feature `default-pie-on-linux` can be handy to exclude default PIE sensitive tests.

Reviewed By: foutrelis, sylvestre.ledru, thesamesam

Differential Revision: https://reviews.llvm.org/D113372
2021-12-14 10:09:00 -08:00
Nico Weber 3950e1be8d [clang] Remove CLANG_ROUND_TRIP_CC1_ARGS and always roundtrip in +assert builds
This removes the ability to disable roundtripping in assert builds.
(Roundtripping happens by default in assert builds both before and after
this patch.)

The CLANG_ROUND_TRIP_CC1_ARGS was added as an escape hatch 9 months ago
in https://reviews.llvm.org/D97462, with a FIXME to remove it eventually.
It's probably time to remove it.

Differential Revision: https://reviews.llvm.org/D114120
2021-11-18 08:31:21 -05:00
Frederic Cambus f0ffff43b7 [CMake] Fix typo in error message for LLD in bootstrap builds.
Reviewed By: xgupta

Differential Revision: https://reviews.llvm.org/D110836
2021-10-06 22:38:12 +05:30
Petr Hosek d893692024 [CMake] Pass through CMAKE_READELF to subbuilds
This matches handling of other CMake variables.

Differential Revision: https://reviews.llvm.org/D110463
2021-09-24 18:20:30 -07:00
Sylvestre Ledru eccd477ce3 Add CMAKE_BUILD_TYPE to the list of BOOTSTRAP_DEFAULT_PASSTHROUGH variables
When building clang in stage2, when -DCMAKE_BUILD_TYPE=RelWithDebInfo is set,
the developer can expect that the stage2 clang is built using the same mode.
Especially as the performances are much worst in debug mode.
(Principle of least astonishment)

Differential Revision: https://reviews.llvm.org/D53014
2021-09-21 10:44:08 +02:00
Alfonso Gregory a2c319fdc6 [LLVM][CMake][NFC] Resolve FIXME: Rename LLVM_CMAKE_PATH to LLVM_CMAKE_DIR throughout the project
This way, we do not need to set LLVM_CMAKE_PATH to LLVM_CMAKE_DIR when (NOT LLVM_CONFIG_FOUND)

Reviewed By: #libc, ldionne

Differential Revision: https://reviews.llvm.org/D107717
2021-09-16 18:29:57 +02:00
Jan Svoboda bb88a5aeee [clang][cli] Round-trip cc1 arguments in assert builds
This patch enables cc1 argument round-trip for assert builds. It can be disabled by building clang with `-DCLANG_ROUND_TRIP_CC1_ARGS=OFF`.

This will be committed only if we reach consensus in https://lists.llvm.org/pipermail/cfe-dev/2021-February/067714.html.

Reviewed By: dexonsmith

Differential Revision: https://reviews.llvm.org/D97462
2021-03-27 17:24:03 +01:00
Shoaib Meenai 33930a0787 [clang] Pass option directly to command. NFC
This code was written back when LLVM's minimum required CMake version
was 2.8.8, and I assume ExternalProject_Add_Step didn't take this option
at that point. It does now though, so we should just use the option.
Setting the _EP_* property is entirely equivalent (and is in fact how
these commands behave internally), but that also feels like an internal
implementation detail we shouldn't be relying on.

Reviewed By: beanz

Differential Revision: https://reviews.llvm.org/D99322
2021-03-25 11:36:06 -07:00
Shoaib Meenai 0135bc996d [clang] Always execute multi-stage install steps
We want installs to be executed even if binaries haven't changed, e.g.
so that we can install to multiple places. This is consistent with how
non-multi-stage install targets (e.g. the regular install-distribution
target) behave.

Reviewed By: phosek

Differential Revision: https://reviews.llvm.org/D99321
2021-03-25 11:36:00 -07:00
Timm Bäder d9ef6bc426 [clang] Disable LTO and LLD on SystemZ for stage3 builds
LLD does not support SystemZ, so it doesn't make sense to use it for
boostrap/stage3 builds, and using LTO in these cases won't work.

Differential Revision: https://reviews.llvm.org/D89942
2021-03-17 15:15:41 +01:00
Markus Böck af2796c76d [test] Add ability to get error messages from CMake for errc substitution
Visual Studios implementation of the C++ Standard Library does not use strerror to produce a message for std::error_code unlike other standard libraries such as libstdc++ or libc++ that might be used.

This patch adds a cmake script that through running a C++ program gets the error messages for the POSIX error codes and passes them onto lit through an optional config parameter.

If the config parameter is not set, or getting the messages failed, due to say a cross compiling configuration without an emulator, it will fall back to using pythons strerror functions.

Differential Revision: https://reviews.llvm.org/D98278
2021-03-15 20:56:08 +01:00
Christopher Tetreault 39970764af [CMake] Require python 3.6 if enabling LLVM test targets
The lit test suite uses python 3.6 features. Rather than a strange
python syntax error upon running the lit tests, we will require the
correct version in CMake.

Reviewed By: serge-sans-paille, yln

Differential Revision: https://reviews.llvm.org/D95635
2021-03-15 09:50:39 -07:00
Martin Storsjö e81d813717 [clang] Don't set CLANG_DEFAULT_UNWINDLIB to none if rtlib is set to compiler-rt
002dd47bdd was meant to not be any
functional change, but it turned out it was.

With CLANG_DEFAULT_RTLIB set to compiler-rt, CLANG_DEFAULT_UNWINDLIB used
to bet set to an empty string, but now was set to "none".

If one only overrode rtlib to libgcc, one previously would get libgcc
as unwind lib, but now didn't. This caused test failures, fixed in
41476d89b8.

Secondly, for the android target, the previous default was to link
libunwind, which this now changed.

Reinstate the exact same behaviour as before (removing the previously
typoed cmake check) and fix the option comment in one place to match
the other one above.

Differential Revision: https://reviews.llvm.org/D98142
2021-03-08 22:29:54 +02:00
Martin Storsjö 002dd47bdd [clang] Fix typos in the default logic for CLANG_DEFAULT_UNWINDLIB
CLANG_DEFAULT_RTLIB had a typo, and libunwind isn't a valid
option for it.

This keeps the actual behaviour from before, defaulting to none if
using compiler-rt as rtlib.

Differential Revision: https://reviews.llvm.org/D98022
2021-03-06 08:50:46 +02:00
Jan Svoboda 225ccf0c50 [clang][cli] Command line round-trip for HeaderSearch options
This patch implements generation of remaining header search arguments.
It's done manually in C++ as opposed to TableGen, because we need the flexibility and don't anticipate reuse.

This patch also tests the generation of header search options via a round-trip. This way, the code gets exercised whenever Clang is built and tested in asserts mode. All `check-clang` tests pass.

Reviewed By: dexonsmith

Differential Revision: https://reviews.llvm.org/D94472
2021-02-04 10:18:34 +01:00
Christopher Tetreault d3e8b9fdc0 Revert "[CMake] Actually require python 3.6 or greater"
There are builders that do not have python 3.6. Revert until this situation can be rectified

This reverts commit 0703b0753c.
2021-01-29 12:03:32 -08:00
Christopher Tetreault 0703b0753c [CMake] Actually require python 3.6 or greater
Previously, CMake would find any version of Python3. However, the project
claims to require 3.6 or greater, and 3.6 features are being used.

Reviewed By: yln

Differential Revision: https://reviews.llvm.org/D95635
2021-01-29 11:47:21 -08:00
Raul Tambre 480643a95c [CMake] Remove dead code setting policies to NEW
cmake_minimum_required(VERSION) calls cmake_policy(VERSION),
which sets all policies up to VERSION to NEW.
LLVM started requiring CMake 3.13 last year, so we can remove
a bunch of code setting policies prior to 3.13 to NEW as it
no longer has any effect.

Reviewed By: phosek, #libunwind, #libc, #libc_abi, ldionne

Differential Revision: https://reviews.llvm.org/D94374
2021-01-19 17:19:36 +02:00
serge-sans-paille 5e31e226b5 Remove Python2 fallback and only advertise Python3 in the doc
Differential Revision: https://www.youtube.com/watch?v=RsL0cipURA0
2020-12-17 15:40:16 +01:00
Arthur Eubanks aafb366210 Reland [CMake][NewPM] Move ENABLE_EXPERIMENTAL_NEW_PASS_MANAGER into llvm/
This allows us to use its value everywhere, rather than just clang. Some
other places, like opt and lld, will use its value soon.

Rename it internally to LLVM_ENABLE_NEW_PASS_MANAGER.

The #define for it is now in llvm-config.h.

The initial land accidentally set the value of
LLVM_ENABLE_NEW_PASS_MANAGER to the string
ENABLE_EXPERIMENTAL_NEW_PASS_MANAGER instead of its value.

Reviewed By: rnk, hans

Differential Revision: https://reviews.llvm.org/D92072
2020-12-01 14:00:32 -08:00
Arthur Eubanks 806a76c001 Revert "[CMake][NewPM] Move ENABLE_EXPERIMENTAL_NEW_PASS_MANAGER into llvm/"
The new pass manager was accidentally enabled by default with this change.

This reverts commit a36bd4c90d.
2020-12-01 13:12:12 -08:00
Arthur Eubanks a36bd4c90d [CMake][NewPM] Move ENABLE_EXPERIMENTAL_NEW_PASS_MANAGER into llvm/
This allows us to use its value everywhere, rather than just clang. Some
other places, like opt and lld, will use its value soon.

The #define for it is now in llvm-config.h.

Reviewed By: rnk, hans

Differential Revision: https://reviews.llvm.org/D92072
2020-12-01 11:42:17 -08:00
Shoaib Meenai 4e4ab8e015 [clang] Limit scope of CLANG_VENDOR definition
It's only used by Version.cpp, so limit the definition to just that one
file instead of making all of Clang recompile if you change CLANG_VENDOR.

Reviewed By: phosek

Differential Revision: https://reviews.llvm.org/D90516
2020-11-02 09:04:43 -08:00
Sylvestre Ledru 0784e17f1b Remove .svn from exclude list as we moved to git
Reviewed By: emaste

Differential Revision: https://reviews.llvm.org/D89859
2020-10-21 16:09:21 +02:00
Joseph Huber d564409946 [OpenMP] Change CMake Configuration to Build for Highest CUDA Architecture by Default
Summary:
This patch changes the CMake files for Clang and Libomptarget to query the
system for its supported CUDA architecture. This makes it much easier for the
user to build optimal code without needing to set the flags manually. This
relies on the now deprecated FindCUDA method in CMake, but full support for
architecture detection is only availible in CMake >3.18

Reviewers: jdoerfert ye-luo

Subscribers: cfe-commits guansong mgorny openmp-commits sstefan1 yaxunl

Tags: #clang #OpenMP

Differential Revision: https://reviews.llvm.org/D87946
2020-10-08 12:09:34 -04:00
Dave Lee b36bdfe5ca [cmake] Centralize LLVM_ENABLE_WARNINGS option
Configure default value of `LLVM_ENABLE_WARNINGS` in `HandleLLVMOptions.cmake`.

`LLVM_ENABLE_WARNINGS` is documented as ON by default, but `HandleLLVMOptions` assumes the default has been set somewhere else. If it has not been explicitly set, then `HandleLLVMOptions` implicitly uses OFF as a default.

This removes the various `option()` declarations in favor of a single declaration in `HandleLLVMOptions`. This will prevent the unwanted use of `-w` that is mentioned in a couple of the comments.

Reviewed By: DavidTruby, #libunwind, JDevlieghere, compnerd

Differential Revision: https://reviews.llvm.org/D87243
2020-09-21 10:23:17 -07:00
Nico Weber 33c9dbbd38 Add an explicit toggle for the static analyzer in clang-tidy
Instead of using CLANG_ENABLE_STATIC_ANALYZER for use of the
static analyzer in both clang and clang-tidy, add a second
toggle CLANG_TIDY_ENABLE_STATIC_ANALYZER.

This allows enabling the static analyzer in clang-tidy while
disabling it in clang.

Differential Revison: https://reviews.llvm.org/D87118
2020-09-10 10:48:17 -04:00
Raul Tambre 86bd8f82cc [CMake] Remove dead FindPythonInterp code
LLVM has bumped the minimum required CMake version to 3.13.4, so this has become dead code.

Reviewed By: #libc, ldionne

Differential Revision: https://reviews.llvm.org/D87189
2020-09-08 15:23:23 +03:00
Petr Hosek 633e3dacf2 [CMake] Print the autodetected host linker version
There's no easy way to find out what the autodetected version is, but
sometimes it may be useful to confirm that the right version is being
used. Print it as CMake status message.

Differential Revision: https://reviews.llvm.org/D85362
2020-08-05 20:22:28 -07:00
Fangrui Song c41a18cf61 [CMake] Default ENABLE_X86_RELAX_RELOCATIONS to ON
This makes clang default to -Wa,-mrelax-relocations=yes, which enables
R_386_GOT32X (GNU as enables it regardless of -mrelax-relocations=) and
R_X86_64_[REX_]GOTPCRELX in MC. The produced object files require GNU ld>=2.26
to link. binutils 2.26 is considered a very old release today.
2020-08-02 23:06:31 -07:00
Michał Górny 21c165de2a [CMake] Pass bugreport URL to standalone clang build
BUG_REPORT_URL is currently used both in LLVM and in Clang but declared
only in the latter.  This means that it's missing in standalone clang
builds and the driver ends up outputting:

  PLEASE submit a bug report to  and include [...]

(note the missing URL)

To fix this, include LLVM_PACKAGE_BUGREPORT in LLVMConfig.cmake
(similarly to how we pass PACKAGE_VERSION) and use it to fill
BUG_REPORT_URL when building clang standalone.

Differential Revision: https://reviews.llvm.org/D84987
2020-08-02 08:32:05 +02:00
Kristina Bessonova ad4ab81dcc [clang][cmake] Force CMAKE_LINKER for multistage build in case of BOOTSTRAP_LLVM_ENABLE_LLD and MSVC
The issue with LLVM_ENABLE_LLD is that it just passes -fuse-ld=lld
to compiler/linker options which makes sense only for those platforms
where cmake invokes a compiler driver for linking. On Windows (MSVC) cmake
invokes the linker directly and requires CMAKE_LINKER to be specified
otherwise it defaults CMAKE_LINKER to be link.exe.

This patch allows BOOTSTRAP_LLVM_ENABLE_LLD to set CMAKE_LINKER in two cases:
* if building for host Windows,
* if crosscompiling for target Windows.

It also skips adding '-fuse-ld=lld' to make lld-link not warning
about 'unknown argument'.

This fixes build with `clang/cmake/caches/DistributionExample.cmake`
on Windows.

Reviewed By: phosek

Differential Revision: https://reviews.llvm.org/D80873
2020-07-28 10:11:52 +02:00
Petr Hosek 64d99cc6ab [CMake] Move find_package(ZLIB) to LLVMConfig
This way, downstream projects don't have to invoke find_package(ZLIB)
reducing the amount of boilerplate.

Differential Revision: https://reviews.llvm.org/D84691
2020-07-27 17:13:55 -07:00
Petr Hosek 10b1b4a231 [CMake] Simplify CMake handling for zlib
Rather than handling zlib handling manually, use find_package from CMake
to find zlib properly. Use this to normalize the LLVM_ENABLE_ZLIB,
HAVE_ZLIB, HAVE_ZLIB_H. Furthermore, require zlib if LLVM_ENABLE_ZLIB is
set to YES, which requires the distributor to explicitly select whether
zlib is enabled or not. This simplifies the CMake handling and usage in
the rest of the tooling.

This is a reland of abb0075 with all followup changes and fixes that
should address issues that were reported in PR44780.

Differential Revision: https://reviews.llvm.org/D79219
2020-07-23 23:05:36 -07:00
Petr Hosek 38c71b7c85 Revert "[CMake] Simplify CMake handling for zlib"
This reverts commit 1d09ecf361 since
it breaks sanitizer bots.
2020-07-23 15:12:42 -07:00
Petr Hosek 1d09ecf361 [CMake] Simplify CMake handling for zlib
Rather than handling zlib handling manually, use find_package from CMake
to find zlib properly. Use this to normalize the LLVM_ENABLE_ZLIB,
HAVE_ZLIB, HAVE_ZLIB_H. Furthermore, require zlib if LLVM_ENABLE_ZLIB is
set to YES, which requires the distributor to explicitly select whether
zlib is enabled or not. This simplifies the CMake handling and usage in
the rest of the tooling.

This is a reland of abb0075 with all followup changes and fixes that
should address issues that were reported in PR44780.

Differential Revision: https://reviews.llvm.org/D79219
2020-07-23 14:47:25 -07:00
Louis Dionne afa1afd410 [CMake] Bump CMake minimum version to 3.13.4
This upgrade should be friction-less because we've already been ensuring
that CMake >= 3.13.4 is used.

This is part of the effort discussed on llvm-dev here:

  http://lists.llvm.org/pipermail/llvm-dev/2020-April/140578.html

Differential Revision: https://reviews.llvm.org/D78648
2020-07-22 14:25:07 -04:00
Michele Scandale 53880b8cb9 [CMake] Make `intrinsics_gen` dependency unconditional.
The `intrinsics_gen` target exists in the CMake exports since r309389
(see LLVMConfig.cmake.in), hence projects can depend on `intrinsics_gen`
even it they are built separately from LLVM.

Reviewed By: MaskRay, JDevlieghere

Differential Revision: https://reviews.llvm.org/D83454
2020-07-17 16:43:17 -07:00
Petr Hosek bcd27d9d73 Revert "[CMake] Simplify CMake handling for zlib"
This reverts commit 8c1a79dc12 because
it fails when zlib isn't installed.
2020-07-14 19:56:10 -07:00
Petr Hosek 8c1a79dc12 [CMake] Simplify CMake handling for zlib
Rather than handling zlib handling manually, use find_package from CMake
to find zlib properly. Use this to normalize the LLVM_ENABLE_ZLIB,
HAVE_ZLIB, HAVE_ZLIB_H. Furthermore, require zlib if LLVM_ENABLE_ZLIB is
set to YES, which requires the distributor to explicitly select whether
zlib is enabled or not. This simplifies the CMake handling and usage in
the rest of the tooling.

This is a reland of abb0075 with all followup changes and fixes that
should address issues that were reported in PR44780.

Differential Revision: https://reviews.llvm.org/D79219
2020-07-14 19:30:08 -07:00