[llvm] perf optimizations for code in getAppleRuntimeUnrollPreferences() (PR #154010)

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

Thanks for the patch. For future reference, please try to make sure the title is in-line with  common practices, i.e. prefixed with `[AArch64]` for AArch64 backend specific changes.

https://github.com/llvm/llvm-project/pull/154010