X86: Lower SMUL_LOHI of v4i32 to pmuldq when SSE4.1 is available.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207318 91177308-0d34-0410-b5e6-96231b3b80d8
X86TTI: i16/i32 vector div with a constant (splat) divisor are reasonably cheap now.

Turn vectorization back on.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207320 91177308-0d34-0410-b5e6-96231b3b80d8