Update preproc for Uno R4

[caternuson]

Potential fix for compile issues on UNO r4 boards:

    Arduino/libraries/Adafruit_ILI9341/Adafruit_ILI9341.cpp:54:10: fatal error: wiring_private.h: No such file or directory

     #include "wiring_private.h"
              ^~~~~~~~~~~~~~~~~~
    compilation terminated.

This is a simple update to the preproc logic.

[caternuson]

@ladyada for review

[mikeysklar]

Tested @caternuson PR from today using a

UNO R4 WiFi
Adafruit 2.8" ili9341 Shield

Built clean and ran smoothly. No modifications to hardware or code.