[msan] Don't put module constructors in comdats.

There is something strange going on with debug info (.eh_frame_hdr)
disappearing when msan.module_ctor are placed in comdat sections.

Moving this functionality under flag, disabled by default.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@263579 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed