This addresses a TODO in foldShuffledIntrinsicOperands to use
isTriviallyVectorizable instead of a hardcoded list of intrinsics, which
in turn allows more intriniscs to be scalarized by VectorCombine.
From what I can tell every intrinsic here should be speculatable so an
assertion was added.
Because this enables intrinsics like abs which have a scalar operand, we
need to also check isVectorIntrinsicWithScalarOpAtArg.
b81d5e06c7