[clang][PAC][ObjC] Merge support for the arm64e block ABI

[ojhunt]

/cherry-pick 716ab03
/cherry-pick dfea6d5

[ojhunt]

There's also a branch with these prs on 21.x: users/ojhunt/ptrauth-block-abi-llvm21

[llvmbot]

Failed to cherry-pick: 716ab03

https://github.com/llvm/llvm-project/actions/runs/16980893222

Please manually backport the fix and push it to your github fork. Once this is done, please create a pull request

[ojhunt]

Fixed by #153725