[llvm] [DebugInfo][RemoveDIs][NFC] Split findDbgDeclares into two functions (PR #77478)

[Jeremy Morse via llvm-commits]

https://github.com/jmorse approved this pull request.

LGTM; best to keep an eye on the compile time tracker too given how hot these functions are.

https://github.com/llvm/llvm-project/pull/77478