[llvm] [InstCombine] [X86] pblendvb intrinsics must be replaced by select when possible (PR #137322)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

Please regenerate Transforms\VectorCombine\AArch64\shrink-types.ll to see if it fixes the CI failure

https://github.com/llvm/llvm-project/pull/137322