Put LayoutError behind reference to shrink result

`LayoutError` is 24 bytes, which is bigger than the `Ok` types, so let's
shrink that.

compiler/rustc_const_eval/src/interpret/intrinsics.rs

@@ -72,7 +72,7 @@ pub(crate) fn eval_nullary_intrinsic<'tcx>(
         }
         sym::pref_align_of => {
             // Correctly handles non-monomorphic calls, so there is no need for ensure_monomorphic_enough.
-            let layout = tcx.layout_of(param_env.and(tp_ty)).map_err(|e| err_inval!(Layout(e)))?;
+            let layout = tcx.layout_of(param_env.and(tp_ty)).map_err(|e| err_inval!(Layout(*e)))?;
             ConstValue::from_target_usize(layout.align.pref.bytes(), &tcx)
         }
         sym::type_id => {