In an excess of confidence, these defines were added to Leonardo's variant.h
3rd party boards sometimes avoid inheriting this variant but they still define USBCON, thus breaking the build
This allows detecting when the USB host sends a break request and what
the value of the request was. See the comments in USBAPI.h for details.
This just modifies the avr core, not the sam core.
Martino Facchin
Nico
Cristian Maglie
Matthijs Kooijman
Zach Eveland