[PAC] Implement the __ptrauth type qualifier.

[asl]

Downstream commit: ahmedbougacha@cc7ba7e

[antoniofrighetto]

Related PR: #100830.

[ahmedbougacha]

Yep, resolved by #100830

[llvmbot]

@llvm/issue-subscribers-clang-codegen

Author: Anton Korobeynikov (asl)

Downstream commit: https://github.com/ahmedbougacha/llvm-project/commit/cc7ba7eb1814e9b254c7d94aa0b78cb0e21acfc5

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Anton Korobeynikov (asl)

Downstream commit: https://github.com/ahmedbougacha/llvm-project/commit/cc7ba7eb1814e9b254c7d94aa0b78cb0e21acfc5