message: Enable 'upgrade_legacy' for MlirFunctionOptimizationPass
  This change enables functionalization of v1 control flow to v2 control flow in
  the beginning of the MlirFunctionOptimizationPass. This avoids v1 control flow
  in the MLIR-based TPU bridge which is not well supported yet.
diff: @@ -127,6 +127,7 @@ Status MlirFunctionOptimizationPass::Run(
  GraphImportConfig import_config;
  import_config.graph_as_function = true;
  import_config.control_outputs = *control_ret_node_names;
  + import_config.upgrade_legacy = true;
  TF_ASSIGN_OR_RETURN(auto module_ref,
  ConvertGraphToMlir(**graph, debug_info, *flib_def,
  import_config, &context));
  