[llvm] [InstCombine] Improve select equiv fold for plain condition (PR #83405)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> Oh，sorry, I reopen it now. I close it because the solution is limit to `single-use select node`, which seems not perfect :)

That is the solution to many combine problems. It's a common and reasonable restriction 

https://github.com/llvm/llvm-project/pull/83405