if(UNIX)

  if(APPLE)
    set(ENV{DYLD_LIBRARY_PATH} "@CMAKE_CURRENT_BINARY_DIR@/python-build/lib")
  else()
    set(ENV{LD_LIBRARY_PATH} "@CMAKE_CURRENT_BINARY_DIR@/python-build/lib")
  endif()

  execute_process(
    COMMAND make
    WORKING_DIRECTORY "@CMAKE_CURRENT_BINARY_DIR@/@proj@-build"
    )

endif()

if(UNIX)
  if( VTK_WRAP_PYTHON )
    if(APPLE)
      set(ENV{DYLD_LIBRARY_PATH} "@CMAKE_CURRENT_BINARY_DIR@/python-build/lib")
    else()
      set(ENV{LD_LIBRARY_PATH} "@CMAKE_CURRENT_BINARY_DIR@/python-build/lib")
    endif()

    execute_process(
      COMMAND make
      WORKING_DIRECTORY "@CMAKE_CURRENT_BINARY_DIR@/@proj@-build"
      )
  endif()
endif()

Allow compilation of VTK with multiple cores...
ENH: Allow compilation of VTK with multiple cores...

if VTK is not built with python