[clang] [Clang] Add __has_target_builtin macro (PR #126324)

[Joseph Huber via cfe-commits]

jhuber6 wrote:

> CC @jdoerfert (we don't have a CUDA maintainer, so I'm not certain who else to tag)

Closest is @Artem-B, there's also a few NVIDIA people floating around like @gonzalobg.

https://github.com/llvm/llvm-project/pull/126324