[clang] [llvm] [NVPTX] Support __usAtomicCAS builtin (PR #99646)

[Artem Belevich via cfe-commits]

Artem-B wrote:

I can land the patch. 

The buildkite failures appear to be unrelated (something in lldb tests).
Let's wait till clang format checks are done.

https://github.com/llvm/llvm-project/pull/99646