Update implementation of OMPT to the specification OpenMP 5.0 Preview 1 (TR4).

The code is tested to work with latest clang, GNU and Intel compiler. The implementation
is optimized for low overhead when no tool is attached shifting the cost to execution with
tool attached.

This patch does not implement OMPT for libomptarget.

Patch by Simon Convent and Joachim Protze

Differential Revision: https://reviews.llvm.org/D38185

llvm-svn: 317085