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

[Kristof Beyls via cfe-commits]

https://github.com/kbeyls approved this pull request.

I just read through the documentation parts of this PR again.
I think that the quality is more than good enough to land, even though there are a few very minor remarks by myself and @DavidSpickett seemingly still open.

I haven't looked again at the details of the implementation, but remember having gone through it quite a long time ago. I'm happy for this PR to land.

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