[clang] [llvm] [ARM] Fix musttail calls (PR #109943)

[Oliver Stannard via cfe-commits]

ostannard wrote:

That rebase picked up a test failure in `CodeGen/AArch64/sme-callee-save-restore-pairs.ll` which looks related to this but isn't, I'll rebase again over the fix.

https://github.com/llvm/llvm-project/pull/109943