[clang] Handle constant "pointers" for `__atomic_always_lock_free`/`__atomic_is_lock_free`. (PR #99340)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman approved this pull request.

LGTM but please add a release note when landing so users know about the changes.

https://github.com/llvm/llvm-project/pull/99340