Correction to enable compilation on platform with only GTK2 libs

	modified:   CMakeLists.txt
	modified:   cmake/OpenCVFindLibsGUI.cmake

cmake/OpenCVFindLibsGUI.cmake

@@ -43,7 +43,9 @@ ocv_clear_vars(HAVE_GTK HAVE_GTK3 HAVE_GTHREAD HAVE_GTKGLEXT)
 if(WITH_GTK AND NOT HAVE_QT)
   if(NOT WITH_GTK_2_X)
     CHECK_MODULE(gtk+-3.0 HAVE_GTK3)
-    set(HAVE_GTK HAVE_GTK3)
+    if(HAVE_GTK3)
+      set(HAVE_GTK TRUE)
+    endif()
   endif()
   if(NOT HAVE_GTK)
     CHECK_MODULE(gtk+-2.0 HAVE_GTK)