builtins.def: New file.

	* config/avr/builtins.def: New file.
	* config/avr/t-avr (avr.o, avr-c.o): Depend on it.
	* config/avr/avr.c (enum avr_builtin_id): Use it.
	(avr_init_builtins): Use it. And use avr_bdesc.
	(bdesc_1arg): Remove.
	(bdesc_2arg): Remove.
	(bdesc_3arg): Remove.
	(struct avr_builtin_description): Add field n_args.
	(avr_bdesc): New static variable using builtins.def.
	(avr_expand_builtin): Use it.
	Don't call avr_expand_delay_cycles if op0 is not CONST_INT.
	(avr_fold_builtin): Fold AVR_BUILTIN_SWAP.
	Don't fold AVR_BUILTIN_INSERT_BITS if arg0 is not INTEGER_CST.

From-SVN: r184616