message: configure.py: enhance systemlibs config
  Allow TF_SYSTEM_LIBS env var to split on spaces or commas.
  Write PREFIX and related variables to bazelrc as well.
diff: @@ -1401,10 +1401,20 @@ def set_grpc_build_flags():
  def set_system_libs_flag(environ_cp):
  syslibs = environ_cp.get('TF_SYSTEM_LIBS', '')
  - syslibs = ','.join(sorted(syslibs.split(',')))
  if syslibs and syslibs != '':
  + if ',' in syslibs:
  + syslibs = ','.join(sorted(syslibs.split(',')))
  + else:
  + syslibs = ','.join(sorted(syslibs.split()))
  write_action_env_to_bazelrc('TF_SYSTEM_LIBS', syslibs)
  + if 'PREFIX' in environ_cp:
  + write_to_bazelrc('build --define=PREFIX=%s' % environ_cp['PREFIX'])
  + if 'LIBDIR' in environ_cp:
  + write_to_bazelrc('build --define=LIBDIR=%s' % environ_cp['LIBDIR'])
  + if 'INCLUDEDIR' in environ_cp:
  + write_to_bazelrc('build --define=INCLUDEDIR=%s' % environ_cp['INCLUDEDIR'])
  +
  def set_windows_build_flags(environ_cp):
  """Set Windows specific build options."""
  