This enables WDT, so sketches do not work.

Port of
https://github.com/arduino/Arduino/commit/6a6ed3d10ad1470283d7771906ce81
ad97fa06f0

Merge branch 'archive_file_path-backwards-compatibility' of https://github.com/sandeepmistry/ArduinoCore-samd

Change digitalPinToInterrupt to return pin, and use g_APinDescription[pin].ulExtInt to map pin inside attachInterrupt/detachInterrupt

This brings things inline with the atachInterrupt documentation for
usage:
attachInterrupt(digitalPinToInterrupt(pin), ISR, mode);

Port of https://github.com/arduino/Arduino/pull/4737

Fix #124

Fix #126

Only enabled if PIN_LED_TXL or PIN_LED_RXL is defined

Port of @tico-tico’s change in
https://github.com/tico-tico/Arduino/commit/a7454b6b5c59187b95c4224aad87
bb01faa06e85 to SAMD core.