[llvm] [VPlan] Simplify VPBlendRecipes to select instructions (PR #133993)

[Luke Lau via llvm-commits]

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lukel97 wrote:

This is no longer vectorized as the VPBlendRecipe is now a Select VPInstruction, which `willGenerateVectors` considers to not generate vectors. I think in this case it makes sense since there's no actual widened recipes in the loop body.

https://github.com/llvm/llvm-project/pull/133993