cooja: Allow CFLAGS to filter thru
cpu/avr/dev/usb: Various minor updates.
Misc AVR updates.
cpu/cc253x: Miscellaneous compiler fixes.
cpu/mc1322x: Minor changes not sure if they are worth keeping.
Add to native-target-osx branch.
cpu/mc1322x: Implemented watchdog.
cpu/mc1322x: Fix for button sensor IRQ.
cpu/mc1322x: Fix LEDs for econotag boards.
Add fallback `_xassert()` implementation.