[clang] [OpenMP] Allow OMP6.0 features. (PR #122108)

[Michael Kruse via cfe-commits]

https://github.com/Meinersbur commented:

I don't think it is necessary to test each value of `-fopenmp-version=` separately, but don't mind either as long it doesn't affect maintanability. 

 * Instead of repeating each clang diagnositic, consider passing multiple values to `-verify`, e.g. `-verify=omp51,omp60`, `-verify=omp51-exact,omp60-or-lafter`

 * Write expected diagnostics on separate lines using `@<relative line>`-syntax

https://github.com/llvm/llvm-project/pull/122108