Teach SanitizerBlacklist to blacklist by SourceLocation. NFC.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@219993 91177308-0d34-0410-b5e6-96231b3b80d8
Appease the buildbots with the special case for non-set variables

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@219994 91177308-0d34-0410-b5e6-96231b3b80d8