SourceMgr: consistently use 'unsigned' for the memory buffer ID type


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212595 91177308-0d34-0410-b5e6-96231b3b80d8
[ASan/Win] Don't instrument COMDAT globals. Properly fixes PR20244.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212596 91177308-0d34-0410-b5e6-96231b3b80d8