[llvm] [BOLT][binary-analysis] Add initial pac-ret gadget scanner (PR #122304)

[Anatoly Trosinenko via llvm-commits]

https://github.com/atrosinenko commented:

Sorry for the delay, added several comments on `NonPacProtectedRetAnalysis.cpp` file, in other respects the PR looks good to me as to a reviewer of the second kind ("People familiar with the pac-ret hardening scheme and AArch64").

https://github.com/llvm/llvm-project/pull/122304