[llvm] [SamplePGO] Optimize the basename matching logic for matching unused profiles (PR #191523)

[Wei Wang via llvm-commits]

apolloww wrote:

Thanks for the compile speed improvement. When I was testing the original PR, the `OrphansByBaseName` was small after filtering out ambiguous names from `FunctionsWithoutProfile`, so I didn't see big compile speed regression. But I think I missed out the case where `OrphansByBaseName` may be big too. 

https://github.com/llvm/llvm-project/pull/191523