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

[Kristof Beyls via llvm-commits]

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@@ -148,6 +149,68 @@ class AArch64MCPlusBuilder : public MCPlusBuilder {
     return false;
   }
 
+  MCPhysReg getAuthenticatedReg(const MCInst &Inst) const override {
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kbeyls wrote:

The regression tests have been added in the latest commit, I believe the work related to this comment is now complete.

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