[llvm] [VPlan] Simplify select with constant condition (PR #150357)

[Luke Lau via llvm-commits]

lukel97 wrote:

> I wonder why InstSimplifyFolder didn't kick in here?

I think some of these are exposed by other simplifications in simplifyRecipe, which tend to just mutate the operands in place rather than creating new instructions via VPBuilder

https://github.com/llvm/llvm-project/pull/150357