[llvm] [AArch64][PAC] Lower ptrauth constants in code for MachO. (PR #97665)

[Daniil Kovalev via llvm-commits]

https://github.com/kovdan01 approved this pull request.

LGTM with a couple of minor nits. Thanks for getting rid of useless `struct AuthStubInfo` in favor of just `const MCExpr *`.

https://github.com/llvm/llvm-project/pull/97665