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

[Michael Kruse via cfe-commits]

https://github.com/Meinersbur commented:

Some nitpicks left. I will LGTM this after you applied them and nobody else has remarks.

Converting all the lines to `@+` syntax would not have been necessary, only those you needed to change. I think it has become a lot more maintainable now. For prefix names, I have no better suggestion.

I'd sign off using `// DEFINE:` as well, but don't require it.

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