message: Only build overlayaxes if USE_OPENGL is enabled
  Fixes
diff: @@ -164,7 +164,10 @@ add_subdirectory(vanderwaals)
  add_subdirectory(wireframe)
  add_subdirectory(force)
  add_subdirectory(meshes)
  +if (USE_OPENGL)
  + # needs some raw OpenGL code
  add_subdirectory(overlayaxes)
  +endif()
  add_subdirectory(vanderwaalsao)
  if (USE_PROTOCALL)
  add_subdirectory(clientserver)
  