Updating implementation of OMPT as specified in OpenMP 5.0 Preview 2 (TR6)

The TR6 document is expected to be publically released around November 15.
This patch does not implement OMPT for libomptarget.

Patch by Simon Convent and Joachim Protze

Differential Revision: https://reviews.llvm.org/D39182

llvm-svn: 317339