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

[Jacob Bramley via llvm-commits]

https://github.com/jacobbramley commented:

Thanks @kbeyls!

This is just a first pass of the implementation, mostly just nits. I'll have a look through the unit tests next week, but I'm already fairly confident after having used it a few times on real code.

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