COMP: use OPENGL_LIBRARIES cmake var since it includes GLU

CMake/FindFLTK.cmake

@@ -332,7 +332,7 @@ IF(NOT FLTK_SKIP_FORMS)
   LIST(APPEND FLTK_LIBRARIES ${FLTK_FORMS_LIBRARY})
 ENDIF()
 IF(NOT FLTK_SKIP_OPENGL)
-  LIST(APPEND FLTK_LIBRARIES ${FLTK_GL_LIBRARY} ${OPENGL_gl_LIBRARY})
+  LIST(APPEND FLTK_LIBRARIES ${FLTK_GL_LIBRARY} ${OPENGL_LIBRARIES})
   LIST(APPEND FLTK_INCLUDE_DIR ${OPENGL_INCLUDE_DIR})
   LIST(REMOVE_DUPLICATES FLTK_INCLUDE_DIR)
 ENDIF()

CMake/ImportFLTK.cmake

@@ -71,7 +71,6 @@ IF(OTB_USE_VISU_GUI)
 		  
         ENDIF(OTB_USE_EXTERNAL_FLTK)
 
-#        SET(OTB_VISU_GUI_LIBRARIES "${FLTK_LIBRARIES};${OPENGL_LIBRARIES};${FLTK_PLATFORM_DEPENDENT_LIBS}")
         SET(OTB_VISU_GUI_LIBRARIES "${FLTK_LIBRARIES}")
         IF(APPLE)
           SET(OTB_VISU_GUI_LIBRARIES "${OTB_VISU_GUI_LIBRARIES};-Wl,-dylib_file,/System/Library/Frameworks/OpenGL.framework/Versions/A/Libraries/libGL.dylib:/System/Library/Frameworks/OpenGL.framework/Versions/A/Libraries/libGL.dylib")