message: cxx: be consistent about frameworks
  On macOS sometimes we get spurious recompilations because the order of
  frameworks changed.  Make their order deterministic.
diff: @@ -79,7 +79,7 @@ class Config:
  self.__libraries = sched.OrderedSet(model.__libraries)
  self.flags = model.flags[:]
  self.ldflags = model.ldflags[:]
  - self._framework = dict(model._framework)
  + self._framework = sched.OrderedSet(model._framework)
  self.__defines = collections.OrderedDict(model.__defines)
  self.__standard = model.__standard
  self.__rpath = model.__rpath[:]
  @@ -263,10 +263,10 @@ class Config:
  self.ldflags.append(f)
  def framework_add(self, name):
  - self._framework[name] = None
  + self._framework.add(name)
  def frameworks(self):
  - return self._framework.keys()
  + return self._framework
  def add_local_include_path(self, path):
  path = drake.Drake.current.prefix / path
  