new_contents: def match(command, settings):
      return (('g++' in command.script or 'clang++' in command.script) and
              ('This file requires compiler and library support for the '
               'ISO C++ 2011 standard.' in command.stderr or
               '-Wc++11-extensions' in command.stderr
              )
             )
  
  
  def get_new_command(command, settings):
      return command.script + ' -std=c++11'
  
subject: Add a `C++11` rule