Use a more direct check for finding out the file type.

No functionality change.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@196811 91177308-0d34-0410-b5e6-96231b3b80d8
Don't add suffixes for stdcall/fastcall on 64 coff.

This matches the behavior of both msvc and mingw.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@196814 91177308-0d34-0410-b5e6-96231b3b80d8