[local-bounds] Ignore volatile operations

Summary:
-fsanitize=local-bounds is very similar to ``object-size`` and
should also ignore volatile pointers.
https://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html#volatile

Reviewers: chandlerc, rsmith

Reviewed By: rsmith

Subscribers: cfe-commits, hiraditya, llvm-commits

Tags: #llvm, #clang

Differential Revision: https://reviews.llvm.org/D78607