[flang] [llvm] [flang][OpenMP] Overhaul implementation of ATOMIC construct (PR #137852)

[via llvm-commits]

https://github.com/NimishMishra commented:

Thanks for the massive work on this patch. I took a look at the parser level changes for now, and tried running a few examples locally. Looks fine overall.

https://github.com/llvm/llvm-project/pull/137852