message: Remove designated initializers, they require C++20.
  This is one step towards getting the Windows build green again.
diff: @@ -1245,10 +1245,11 @@ Status ValidateGraph(const Graph* graph,
  }
  if (std::shared_ptr<AbstractStackTrace> stack_trace =
  node->GetStackTrace()) {
  - absl::StrAppend(&errmsg, "\nThe op is created at: \n",
  - stack_trace->ToString({.show_line_contents = true,
  - .filter_common_prefix = true,
  - .drop_internal_frames = true}));
  + absl::StrAppend(
  + &errmsg, "\nThe op is created at: \n",
  + stack_trace->ToString({/*show_line_contents =*/true,
  + /*filter_common_prefix =*/true,
  + /*drop_internal_frames =*/true}));
  }
  return errors::InvalidArgument(errmsg);
  