eliminate compiler warnings

samples/cpp/detect_mser.cpp

@@ -97,8 +97,10 @@ static String Legende(MSERParams &pAct)
 }
 
 
+#ifdef HAVE_OPENGL
 const int win_width = 800;
 const int win_height = 640;
+#endif
 bool    rotateEnable=true;
 bool    keyPressed=false;
 

samples/cpp/videostab.cpp

@@ -224,6 +224,8 @@ public:
             kbest->setOutlierRejector(outlierRejector);
             return kbest;
         }
+#else
+        CV_Assert(gpu == false && "CUDA modules are not available");
 #endif
 
         Ptr<KeypointBasedMotionEstimator> kbest = makePtr<KeypointBasedMotionEstimator>(est);
@@ -265,6 +267,8 @@ public:
             kbest->setOutlierRejector(outlierRejector);
             return kbest;
         }
+#else
+        CV_Assert(gpu == false && "CUDA modules are not available");
 #endif
 
         Ptr<KeypointBasedMotionEstimator> kbest = makePtr<KeypointBasedMotionEstimator>(est);