FIX: Workaround a problem in VTK:  I need to CONFIGURE VTKConfig.cmake in non-immediate mode so that it can pick the variables that are set in SUBDIRS.  On the other hand, CMake's FindVTK is looking for VTKConfig.cmake to  find VTK. In an app like ParaViewComplete, VTK is accessed through  SUBDIRS(), Xdmf too. If we are in non-immediate mode, at the time  we go into the Xdmf subdir, VTKConfig.cmake has not been created, hence  VTK is not found.