[llvm] Fix: Distinguish CFI Metadata Checks in MergeFunctions Pass (PR #65963)

[Duncan P. N. Exon Smith via llvm-commits]

https://github.com/dexonsmith commented:

A few more style nits; after that, LGTM again, but let's wait for @nikic to take another look (thanks for catching the missing `isDistinct()` check...)

https://github.com/llvm/llvm-project/pull/65963