[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:

Thanks for noticing! The original code here was written before these instructions were fully defined...
I've added them now in commit `f44f9bf`, but still need to write regression tests for these instructions.

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