Fix warning 'catching polymorphic type by value'

src/libstore/build/create-derivation-and-realise-goal.cc

@@ -96,7 +96,7 @@ void CreateDerivationAndRealiseGoal::getDerivation()
         auto drvPath = StorePath::dummy;
         try {
             drvPath = resolveDerivedPath(worker.store, *drvReq);
-        } catch (MissingRealisation) {
+        } catch (MissingRealisation &) {
             return std::nullopt;
         }
         return worker.evalStore.isValidPath(drvPath) || worker.store.isValidPath(drvPath)

src/libutil/util.cc

@@ -60,7 +60,7 @@ void initLibUtil() {
     bool caught = false;
     try {
         throwExceptionSelfCheck();
-    } catch (nix::Error _e) {
+    } catch (const nix::Error & _e) {
         caught = true;
     }
     // This is not actually the main point of this check, but let's make sure anyway: