the __attribute__ ((format (printf, 1, 0))) declaration remove the following
compilation warning:
warning: function 'osmo_panic' might be a candidate for 'gnu_printf' format
attribute [-Wsuggest-attribute=format]
osmo_panic_default(fmt, args);
This way we can easily check with 'diff' for differences in our code and
Atmel softpack. Also, this layout is more suitable for building various
different firmware images (e.g. factory-test, dfu-loader, main
application) for a variety of different boards (simtrace, owhw, qmod).