[clang] [AArch64][PAC] Support ptrauth builtins and -fptrauth-intrinsics. (PR #65996)

[David Spickett via cfe-commits]

DavidSpickett wrote:

Maybe I just need to learn how to use Github, but did half the document disappear?

I see a reference to the attacks section `See the section on `Attacks on pointer authentication`_ for more information.` but the section is gone from the diff even in a private window.

https://github.com/llvm/llvm-project/pull/65996