message: Add i64x2.mul.
  Remove commented-out i8x16.mul. This no longer exists in the SIMD proposal.
diff: @@ -2621,14 +2621,6 @@ impl<'ctx, 'a> LLVMFunctionCodeGenerator<'ctx, 'a> {
  let res = self.builder.build_int_mul(v1, v2, "");
  self.state.push1(res);
  }
  - // Operator::I8x16Mul => {
  - // let ((v1, i1), (v2, i2)) = self.state.pop2_extra()?;
  - // let (v1, _) = self.v128_into_i8x16(v1, i1);
  - // let (v2, _) = self.v128_into_i8x16(v2, i2);
  - // let res = self.builder.build_int_mul(v1, v2, "");
  - // let res = self.builder.build_bitcast(res, self.intrinsics.i128_ty, "");
  - // self.state.push1(res);
  - // }
  Operator::I16x8Mul => {
  let ((v1, i1), (v2, i2)) = self.state.pop2_extra()?;
  let (v1, _) = self.v128_into_i16x8(v1, i1);
  @@ -2645,6 +2637,14 @@ impl<'ctx, 'a> LLVMFunctionCodeGenerator<'ctx, 'a> {
  let res = self.builder.build_bitcast(res, self.intrinsics.i128_ty, "");
  self.state.push1(res);
  }
  + Operator::I64x2Mul => {
  + let ((v1, i1), (v2, i2)) = self.state.pop2_extra()?;
  + let (v1, _) = self.v128_into_i64x2(v1, i1);
  + let (v2, _) = self.v128_into_i64x2(v2, i2);
  + let res = self.builder.build_int_mul(v1, v2, "");
  + let res = self.builder.build_bitcast(res, self.intrinsics.i128_ty, "");
  + self.state.push1(res);
  + }
  Operator::I32DivS | Operator::I64DivS => {
  let ((v1, i1), (v2, i2)) = self.state.pop2_extra()?;
  let v1 = self.apply_pending_canonicalization(v1, i1);
  