GPS - Fix build for non-GPS enabled targets.

src/main/mw.c

@@ -614,9 +614,11 @@ void loop(void)
         // if GPS feature is enabled, gpsThread() will be called at some intervals to check for stuck
         // hardware, wrong baud rates, init GPS if needed, etc. Don't use SENSOR_GPS here as gpsThread() can and will
         // change this based on available hardware
+#ifdef GPS
         if (feature(FEATURE_GPS)) {
             gpsThread();
         }
+#endif
     }
 
     currentTime = micros();