[OpenMP][OMPT] Fix compile-time assertion in ompt-multiplex.h

The compile-time assertion is supposed to prevent double-free caused by
unexpected combination of preprocessor defines passed by an OMPT tool.
The current defines are not used, so this patch replaces the check with
macros actually used in ompt-multiplex.h

Reported by: Semih Burak

Differential Revision: https://reviews.llvm.org/D104633