Decouple llvm::SpecialCaseList text representation and its LLVM IR semantics.

Decouple llvm::SpecialCaseList text representation and its LLVM IR semantics.

Turn llvm::SpecialCaseList into a simple class that parses text files in
a specified format and knows nothing about LLVM IR. Move this class into
LLVMSupport library. Implement two users of this class:
  * DFSanABIList in DFSan instrumentation pass.
  * SanitizerBlacklist in Clang CodeGen library.
The latter will be modified to use actual source-level information from frontend
(source file names) instead of unstable LLVM IR things (LLVM Module identifier).

Remove dependency edge from ClangCodeGen/ClangDriver to LLVMTransformUtils.

No functionality change.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212643 91177308-0d34-0410-b5e6-96231b3b80d8