Cleanup stdcall / fastcall name mangling.
This should fix alot of problems we saw so far, e.g. PRs 5851 & 2936

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@95980 91177308-0d34-0410-b5e6-96231b3b80d8
9 files changed