[clang] [PAC][clang] Define `PointerAuthQualifier` and `PointerAuthenticationMode` (PR #84384)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman commented:

The changes have no testing associated with them -- what's the plan for that?

https://github.com/llvm/llvm-project/pull/84384