Fix CSU OMP compilation issues with pgi/intel

We throw a c99 compatible flag by default which caused a warning message from the intel compiler. This PR removes that flag from the OpenMP tests from CSU.

The PGI compiler doesn't support the -fopenmp flag, and there's not a clean way to choose different flags based on the compiler (at least not yet). For now, disable testing with PGI for these CSU OpenMP tests.

These changes won't effect the online performance results.