[clang] [clang][CodeGen] Emit atomic IR instead of libcalls for misaligned po… (PR #73176)

[Eli Friedman via cfe-commits]

efriedma-quic wrote:

As a historical note, when I first wrote the support for atomics, it was under a model where LLVM IR only modeled legal atomics, and clang lowered illegal atomics to libcalls.  This was changed a few years later to generalize atomics in LLVM IR to support arbitrary atomic ops lowered to libcalls.  But there are still a few inconsistencies resulting from this, I think.

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