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

[Kristof Beyls via llvm-commits]

https://github.com/kbeyls commented:

Thank you for fixing this!

Let me ping @eugenis as the original author of this code. @eugenis : we had to change the code sequence produced for TagLoop pseudos in #5e612bc291 to avoid a conflict with SpeculativeLoadHardening. Before the TagLoop pseudos did not clobber NZCV, now they do.

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