Well there might be something broken with your setup, I checked the Adafruit_mfGFX.cpp file for uninitialized line variable and it should be defined in all cases. And the rest of warnings seems somewhat fishy too. I seen similar errors solved using this code on top of your code:
#pragma SPARK_NO_PREPROCESSOR
#include "application.h"
Not sure if it helps, but worth the try.
There is some rather advanced thread about the problem: