[clang] [OpenACC][CIR] Implement atomic-write lowering (PR #164627)

[Erich Keane via cfe-commits]

erichkeane wrote:

https://github.com/llvm/llvm-project/pull/164828

Fix is there ^^ Set up as auto-merge, so will merge as soon as CI is happy.

https://github.com/llvm/llvm-project/pull/164627