[llvm] [AArch64] Fix tryMergeAdjacentSTG function in PrologEpilog pass (PR #68873)

[Kristof Beyls via llvm-commits]

================
@@ -3703,6 +3703,17 @@ bool isMergeableStackTaggingInstruction(MachineInstr &MI, int64_t &Offset,
   return true;
 }
 
+bool isNZCVLiveOut(MachineBasicBlock &MBB) {
----------------
kbeyls wrote:

I'm wondering why this need a new function to be implemented.
Wouldn't calling `MBB.isLiveOut(MBB, AArch64::NZCV)` work the same as calling `isNZCVLiveOut(MBB)`?

https://github.com/llvm/llvm-project/pull/68873