[clang] [clang][OpenMP] Fix/enforce order-concurrent-nestable rules (PR #135463)

[Ernesto Su via cfe-commits]

ErnestoSu wrote:

@alexey-bataev @zahiraam Thanks so much for your review and approval! Is there anything else I need to do before this PR can be merged by one of you?

https://github.com/llvm/llvm-project/pull/135463