Otherwise if 'ld' is an older system LLD (FreeBSD; or if someone adds 'ld' to
point to an LLD from a different installation) which does not support the
current ModuleSummaryIndex::BitCodeSummaryVersion, the test will fail.
Add lit feature 'binutils_lto'. GNU ld is more common than GNU gold, so
we can just require 'is_binutils_lto_supported' to additionally support GNU ld.
Reviewed By: myhsu
Differential Revision: https://reviews.llvm.org/D84133
Similar to the reason behind moving __llvm_profile_filename into a
separate file[1]. When users try to use Full LTO with BFD linker to
generate IR level PGO profile, the __llvm_profile_raw_version variable,
which is used for marking instrumentation level, generated by frontend
would somehow conflict with the weak symbol provided by profiling
runtime.
In most of the cases, BFD linkers will pick profiling runtime's weak symbol
as the real definition and thus generate the incorrect instrumentation
level metadata in the final executables.
Moving __llvm_profile_raw_version into a separate file would make
linkers not seeing the weak symbol in the archive unless the frontend
doesn't generate one.
[1] https://reviews.llvm.org/D34797
Differential Revision: https://reviews.llvm.org/D83967
Fangrui Song