Changed LED_BUILTIN to a macro to better support boards that do not have a built-in LED.

Fixes #758

Author: cmaglie

hardware/arduino/variants/mega/pins_arduino.h

@@ -39,7 +39,7 @@ static const uint8_t SCK  = 52;
 
 static const uint8_t SDA = 20;
 static const uint8_t SCL = 21;
-static const uint8_t LED_BUILTIN = 13;
+#define LED_BUILTIN 13
 
 static const uint8_t A0 = 54;
 static const uint8_t A1 = 55;
@@ -360,4 +360,4 @@ const uint8_t PROGMEM digital_pin_to_timer_PGM[] = {
 
 #endif
 
-#endif
+#endif