message: cxx: Support C++ 17.
diff: @@ -468,6 +468,7 @@ class Config:
  def __str__(self):
  return 'C++ %s' % self.__name
  + cxx_17 = Standard('17')
  cxx_14 = Standard('14')
  cxx_11 = Standard('11')
  cxx_0x = Standard('0x')
  @@ -805,6 +806,8 @@ class GccToolkit(Toolkit):
  res.append('-std=c++11')
  else:
  res.append('-std=c++14')
  + elif std is Config.cxx_17:
  + res.append('-std=c++17')
  else:
  raise Exception('Unknown C++ standard: %s' % std)
  if cfg.warnings:
  