[PGO] Improve hash-mismatch warning message

This patch improves FDO hash-mismatch handling:
(1) filter out warnings to weak functions.
Weak functions definition will be overridden by a strong definition by linker.
The hash mismatch in profile use compilation is expected.
Make the profile hash mismatch warning under the existing option (default true).

(2) add an option to trace the hash of functions with the specific string.
Note that an empty string parameter will trace all functions.

Differential Revision: https://reviews.llvm.org/D129002