code: def _subst_libs(env, libs):
      
      if SCons.Util.is_String(libs):
          libs = env.subst(libs)
          if SCons.Util.is_String(libs):
              libs = libs.split()
      elif SCons.Util.is_Sequence(libs):
          _libs = []
          for l in libs:
              _libs += _subst_libs(env, l)
          libs = _libs
      else:
          # libs is an object (Node, for example)
          libs = [libs]
      return libs
docs: Substitute environment variables and split into list.