[clang] [clang][CodeGen] Emit atomic IR in place of optimized libcalls. (PR #73176)

[Eli Friedman via cfe-commits]

efriedma-quic wrote:

Looks like a bug in the SPARC backend.  https://github.com/llvm/llvm-project/pull/73176#pullrequestreview-1811677691  indicated that atomic expansion was working correctly for all backends, but I guess it isn't working correctly on SPARC.

https://github.com/llvm/llvm-project/pull/73176