[flang] [llvm] [mlir][llvm][OpenMP] Emit llvm.stacksave and llvm.stackrestore in __atomic_compare_exchange (PR #132888)

[Michael Kruse via llvm-commits]

https://github.com/Meinersbur requested changes to this pull request.

stacksave/stackrestore is for dynamically-sized allocas. If you don't have dynamically-sized allocas, don't use them. Normqal allocas **must** be emitted into the AllocaInsertPt (as done in #101966).

https://github.com/llvm/llvm-project/pull/132888