Fix strict build

Signed-off-by: falkTX <falktx@falktx.com>

source/backend/engine/CarlaEngineNative.cpp

@@ -1743,6 +1743,8 @@ private:
 
             for (; msgMgr->dispatchNextMessageOnSystemQueue(true);) {}
         }
+
+        CARLA_DECLARE_NON_COPY_STRUCT(ScopedJuceMessageThreadRunner)
     };
 #endif