[llvm] [DebugInfo][LoopLoadElim] Fix missing debug location updates (PR #91839)

[Orlando Cazalet-Hyams via llvm-commits]

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

As @jryans mentions in the inline comments, it looks like we've reached a consensus that the eliminated `load`'s debug location is indeed suitable for the `phi`. If someone comes back to this and strongly disagrees we can look at it again and make adjustments as necessary.

LGTM, thanks!

https://github.com/llvm/llvm-project/pull/91839