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

[Jonathan Cohen via llvm-commits]

https://github.com/jcohen-apple approved this pull request.

LGTM - does not change the functionality of the unroll preferences, but just does the cheaper unroll count check first.

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