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

[Anton Korobeynikov via llvm-commits]

asl wrote:

@efriedma-quic But it is 'Constant`, not `ConstantExpr`. So in this sense it is not different from e.g. `DSOLocalEquivalent` or `NoCFIValue` that we are already having in tree. Or maybe I'm missing what do you mean?

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