message: cxx: style change
  avoid negated conditions
diff: @@ -1001,13 +1001,12 @@ class GccToolkit(Toolkit):
  def rpath(self, path):
  path = drake.Path(path)
  - if not path.absolute():
  - if self.os is drake.os.macos:
  + if path.absolute():
  + return path
  + elif self.os is drake.os.macos:
  return drake.Path('@loader_path') / path
  else:
  return drake.Path('$ORIGIN') / path
  - else:
  - return path
  def __split(self):
  if self.__splitted is None:
  