[llvm] Fix performance bug in buildLocationList (PR #109343)

[Krzysztof Pszeniczny via llvm-commits]

amharc wrote:

I think the logic in this PR is correct: the comment for `buildLocationList` says "If the resulting list has only one entry that is valid throughout variable's scope return true" and this seems to be the case with this PR too. I'm not a debug info expert though.

https://github.com/llvm/llvm-project/pull/109343