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

[Joseph Huber via cfe-commits]

jhuber6 wrote:

> Sorry, I kind of got lost in the above discussion. Are additional changes required in Clang to parse builtins unsupported on the current target to make sure we don't break anything or is only changing the result of `__has_builtin` acceptable?

I believe the conclusion was that we should emit the builtin functions, but `__has_builtin` should return false for builtins only present in the aux triple. For the one test that complicates this behavior, I don't think the use-case is completely well-formed but was hoping @boomanaiden154 would chime in on what the expected behavior is. I would prefer if this is just a simply check for "not in aux builtin".

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