[flang] [llvm] [flang][OpenACC][OpenMP] Separate implementations of ATOMIC constructs (PR #137517)

[Razvan Lupusoru via llvm-commits]

https://github.com/razvanlupusoru approved this pull request.

Would you mind clarifying which atomic features from OpenMP 6.0 cause the difference between OpenMP and OpenACC atomics to widen that they need separated out?

https://github.com/llvm/llvm-project/pull/137517