message: [TF2XLA] Don't change output port for control dependency in CopySubgraph.
  If the output is being squashed then we want control output 0, except where the
  input is a control dependency.
diff: @@ -130,7 +130,9 @@ Status CopySubgraph(const Graph& graph, const Frame* frame,
  stack.push_back(src);
  }
  Node* src_copy = (*node_map)[e->src()->id()];
  - int src_output = squash_src_outputs[e->src()->id()] ? 0 : e->src_output();
  + int src_output = squash_src_outputs[e->src()->id()] && !e->IsControlEdge()
  + ? 0
  + : e->src_output();
  Node* dst_copy = (*node_map)[e->dst()->id()];
  output->AddEdge(src_copy, src_output, dst_copy, e->dst_input());
  }
  