keep arduino incompatible BUILTIN_LED

Author: tuxedo0801

variants/adafruit/pins_arduino.h

@@ -43,6 +43,7 @@ static const uint8_t MISO  = 12;
 static const uint8_t SCK   = 14;
 
 static const uint8_t LED_BUILTIN = 0;
+static const uint8_t BUILTIN_LED = 0;
 
 static const uint8_t A0 = 17;