message: Fix compiler warning about unused variable
diff: @@ -711,7 +711,8 @@ Status ArgNumType(AttrSlice attrs, const OpDef::ArgDef& arg_def,
  REGISTER_OP_GRADIENT_UNIQ(ctr, name, fn)
  #define REGISTER_OP_GRADIENT_UNIQ(ctr, name, fn) \
  - static bool unused_grad_##ctr = SHOULD_REGISTER_OP_GRADIENT && \
  + static bool unused_grad_##ctr TF_ATTRIBUTE_UNUSED = \
  + SHOULD_REGISTER_OP_GRADIENT && \
  ::tensorflow::gradient::RegisterOp(name, fn)
  namespace gradient {
  