tsan: add OnFinalize() callback for frontends


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@173915 91177308-0d34-0410-b5e6-96231b3b80d8
tsan: introduce a helped macro CPP_WEAK (Go linker does not support weak symbols)


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@173917 91177308-0d34-0410-b5e6-96231b3b80d8
[msan] Remove an extra #ifdef.

__has_feature is always defined at this point.


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@173920 91177308-0d34-0410-b5e6-96231b3b80d8