[clang] [Clang] __has_builtin should return false for aux triple builtins (PR #121839)

[Joseph Huber via cfe-commits]

jhuber6 wrote:

Ah, I see how it is. And it probably worked in the NVPTX / AMDGCN case because we had valid code paths. This is definitely something that should be fixed, because it makes no sense to say a builtin is available if you can't even use it. Though offloading languages do tend to hate anything that lets users peel back the layers and see them as two separate compile jobs.

https://github.com/llvm/llvm-project/pull/121839