[clang] [clang] Add an ABI_EXTENSION concept that is testable under -pedantic… (PR #153506)

[Oliver Hunt via cfe-commits]

ojhunt wrote:

Closing, as for the current critical case (ptrauth) we're keeping the tests as a feature when the target is arm64e, and adding a ``__PTRAUTH__`` define that will be the correct test going forward.

https://github.com/llvm/llvm-project/pull/153506