[llvm] [InstCombine] Improve coverage of `foldSelectValueEquivalence` (PR #88298)

[via llvm-commits]

goldsteinn wrote:

> What was the motivating case from #87275?

Yes, although we are waiting to get @dtcxzyw's results to see if it has other benefits.

https://github.com/llvm/llvm-project/pull/88298