message: added compile time notification message
  Added the pragma message directive to notify the user of the absence of CMSIS-NN library
diff: @@ -236,6 +236,8 @@ TfLiteStatus EvalQuantizedPerChannel(
  }
  }
  #else
  +#pragma message( \
  + "CMSIS-NN optimization for conv not available for this target. Using reference kernel.")
  reference_integer_ops::ConvPerChannel(
  op_params, data->per_channel_output_multiplier,
  