[llvm] [InstCombine] Improve coverage of `foldSelectValueEquivalence` for non-constants (PR #94719)

[via llvm-commits]

goldsteinn wrote:

Ran ~5million csmith tests. No inf loops or bad codegen. Although note only got different resulting IR ~100 times over all the tests.

https://github.com/llvm/llvm-project/pull/94719