Add constness to ParamEnv

This now causes a lot of queries to be executed twice, as reveal_all forces NotConst

compiler/rustc_trait_selection/src/traits/auto_trait.rs

@@ -370,12 +370,17 @@ impl AutoTraitFinder<'tcx> {
                 computed_preds.clone().chain(user_computed_preds.iter().cloned()),
             )
             .map(|o| o.predicate);
-            new_env = ty::ParamEnv::new(tcx.mk_predicates(normalized_preds), param_env.reveal());
+            new_env = ty::ParamEnv::new(
+                tcx.mk_predicates(normalized_preds),
+                param_env.reveal(),
+                param_env.constness(),
+            );
         }
 
         let final_user_env = ty::ParamEnv::new(
             tcx.mk_predicates(user_computed_preds.into_iter()),
             user_env.reveal(),
+            user_env.constness(),
         );
         debug!(
             "evaluate_nested_obligations(ty={:?}, trait_did={:?}): succeeded with '{:?}' \