If the host compiler is MSVC or clang-cl, then the compiler used to
buidl the runtimes will be clang-cl, and it doesn't support either of
those flags.
Worse, because -isystem is a space separated flag, it causes all cmake
try_compile tests to fail, so none of the -Wno-* flags make it to the
compiler in libcxx. I noticed that we weren't passing
-Wno-user-defined-literals to clang-cl and were getting warnings in the
build, and this fixes that for me.
Differential Revision: https://reviews.llvm.org/D94817
Previously, llvm/runtimes/CMakeLists.txt played two different roles:
1. host side which could used to set up the build of runtimes for
different targets in the right order;
2. target side to build the runtimes for the specified target.
This change splits llvm/runtimes/CMakeLists.txt and moves the target
side to runtimes/CMakeLists laying down the foundation for the "A vision
for building the runtimes" proposal. From the user perspective, there
shouldn't be any visible difference at the moment.
Differential Revision: https://reviews.llvm.org/D93408
Reid Kleckner