message: Don't define a builder in case of cyclic dependency.
diff: @@ -1965,13 +1965,12 @@ class Builder:
  for source in srcs:
  self.__sources[source._BaseNode__name] = source
  source.consumers.append(self)
  - self.__targets = []
  - for dst in dsts:
  + self.__targets = list(dsts)
  + drake.Drake.current._Drake__register_dependency(list(self.__sources.values()), self.__targets)
  + for dst in self.__targets:
  if dst.builder is not None:
  raise BuilderRedefinition(dst, dst.builder, self)
  - self.__targets.append(dst)
  dst.builder = self
  - drake.Drake.current._Drake__register_dependency(list(self.__sources.values()), self.__targets)
  self.uid = Builder.uid
  Builder.uid += 1
  Builder.builders.append(self)
  