Sanitiser common, using u64 type for GetTid on posix systems

Summary: Moving from ptr to u64 for GetTid posix implementation.
[FreeBSD] Moving from pthread_self to thr_self more appropriate to get thread ID.

Patch by: David CARLIER

Reviewers: krytarowski, vitalybuka

Reviewed By: vitalybuka

Subscribers: kubamracek, llvm-commits, #sanitizers

Differential Revision: https://reviews.llvm.org/D43998

llvm-svn: 326647