[Intrinsic] Expand SMULFIX to MUL, MULH[US], or [US]MUL_LOHI on vector arguments
r zero scale SMULFIX, expand into MUL which produces better code for X86.
For vector arguments, expand into MUL if SMULFIX is provided with a zero scale.
Otherwise, expand into MULH[US] or [US]MUL_LOHI.
Differential Revision: https://reviews.llvm.org/D56987