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

[Peter Smith via llvm-commits]

https://github.com/smithp35 commented:

A first pass through the comments/documentation. I've not had a chance to go through the code yet.

Although out of scope for this patch, I'm thinking it will be worth working on a mechanism to exclude certain functions from the analysis. For example if someone has used the branch protection attribute to explicitly exclude a function from branch-protection. An obvious starting point would be some kind of exclude list file, possibly using the same format as the sanitizers.

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