[HWASAN][LSAN] Fix false positive memory leak reports on X86_64

Before this patch when running HWASAN on x86_64 with with memory tagging support we got a bunch of false memory leak reports. The reason for that is that the heuristic used to detect if an 8 bytes could be a user pointer was not valid when memory tagging is used as the top byte could contain non-zero information.

Reviewed By: vitalybuka

Differential Revision: https://reviews.llvm.org/D155338