Fix CMakeLists.txt

CMakeLists.txt

@@ -52,6 +52,7 @@ MESSAGE(STATUS "Looking for Qt ${DESIRED_QT_VERSION_MAJOR}.")
 SET(CMAKE_INCLUDE_CURRENT_DIR ON)
 IF(USE_QT4)
   FIND_PACKAGE(Qt4 REQUIRED QtCore QtGui QtOpenGl QtNetwork)
+  ADD_DEFINITIONS(-DUSE_QT4)
   SET(PKG_CONFIG_EXTRA "qtversion: ${QT_VERSION_MAJOR}.${QT_VERSION_MINOR}.${QT_VERSION_PATCH}")
 ELSE(USE_QT4)
   FOREACH (component "Core" "Widgets" "Gui" "OpenGL" "Concurrent" "Network")