[llvm] [PAC][IR][AArch64] Add "ptrauth(...)" Constant to represent signed pointers. (PR #85738)

[Ahmed Bougacha via llvm-commits]

ahmedbougacha wrote:

Thanks for taking a look!  e47a75a should address the comments, and 48a946c does a couple other minor cleanups.  Looking at this again, we can make the discriminator components optional while it's still easy, and re-order them to have the simple integer-discriminator-only case shorter;  did that in c6638c7.
We had a couple RFCs in the past but I'll make a fresh thread.

https://github.com/llvm/llvm-project/pull/85738