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

[James Y Knight via cfe-commits]

jyknight wrote:

BTW, please don't rebase/amend commits and force-push, it makes a it extremely difficult to review the changes since the previous review -- especially if the new changes are commingled with a rebase.

Much better to simply push new commits on top of your existing branch. And if you need an updated baseline, you can `git merge origin/main` in your PR branch.

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