[OpenMP][Tool] Improving stack trace for Archer

The OpenMP runtime is not instrumented, so entering the runtime leaves no hint
on the source line of the pragma on ThreadSanitizer's function stack.

This patch adds function entry/exit annotations for OpenMP parallel regions,
and synchronization regions (barrier, taskwait, taskgroup).

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D70408