message: Implement unchecked_mul intrinsic
diff: @@ -436,12 +436,13 @@ fn codegen_regular_intrinsic_call<'tcx>(
  ret.write_cvalue(fx, CValue::by_val(align, usize_layout));
  };
  - unchecked_add | unchecked_sub | unchecked_div | exact_div | unchecked_rem
  + unchecked_add | unchecked_sub | unchecked_mul | unchecked_div | exact_div | unchecked_rem
  | unchecked_shl | unchecked_shr, (c x, c y) {
  // FIXME trap on overflow
  let bin_op = match intrinsic {
  sym::unchecked_add => BinOp::Add,
  sym::unchecked_sub => BinOp::Sub,
  + sym::unchecked_mul => BinOp::Mul,
  sym::unchecked_div | sym::exact_div => BinOp::Div,
  sym::unchecked_rem => BinOp::Rem,
  sym::unchecked_shl => BinOp::Shl,
  