Add ATmega1280 and ATxmega128a3 board descriptions, plus minor tidy-ups.

	* build-all.sh: Add more configure options, including default
	DWARF2 for consistency with Atmel India.
	* dejagnu/baseboards/atmega128-sim.exp: Layout tidy up/
	* dejagnu/baseboards/atmega1280-sim.exp: New board, based on
	specification by Pitchumani S.
	* dejagnu/baseboards/atxmega128a3-sim.exp: Likewise.
	* run-tests/sh: do_c++ -> do_cpp.