[clang] [llvm] [arm64e] Add a builtin + intrinsic for arm64e PAuth_LR: __builtin_ptr_auth_auth_with_pc_and_resign (PR #202742)

[Anatoly Trosinenko via cfe-commits]

atrosinenko wrote:

Considering the "input" discriminator being fed into `AUTPCPAC` pseudo via a single implicit operand, is it at all expected to be computed as a blend "in a foreseeable future"? Do I get it right that due to specifics of the signing schema involving the PC value, for now `AUTDisc` is always expected to be the value of SP at the function entry?

https://github.com/llvm/llvm-project/pull/202742