Add explicit error for USB XInput setting

Author: dmadison

src/XInput.cpp

@@ -35,6 +35,10 @@
 	(defined(__MK20DX256__) || defined(__MKL26Z64__) || \
 	 defined(__MK64FX512__) || defined(__MK66FX1M0__))
 
+	#ifndef USB_XINPUT
+	#error "USB type is not set to XInput in boards menu!"
+	#endif
+
 #else
 #error "Not a supported board! Must use Teensy 3.1/3.2, LC, 3.5, or 3.6"
 #endif