Emulate C99/C++11 __func__ for Visual C++.


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@202296 91177308-0d34-0410-b5e6-96231b3b80d8
Reapply r201910. MSVC gets __func__ defined explicitly, even though it
can't build anything here.


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@202297 91177308-0d34-0410-b5e6-96231b3b80d8
Undef helper macros after using them.


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@202298 91177308-0d34-0410-b5e6-96231b3b80d8