[clang] Add clang_elementwise_builtin_alias (PR #86175)

[Justin Bogner via cfe-commits]

bogner wrote:

Thanks for working on this, but I think that what this shows is that the complexity of adding this elementwise alias builtin isn't quite justified by the utility. It's certainly convenient to be able to specify the builtins this way, but validation is a lot more complicated and I think this will be hard to test. Maybe we should consider this a successful experiment but drop the idea for now unless we run into a situation where we really need it in the future.

https://github.com/llvm/llvm-project/pull/86175