re PR target/56445 (avr.c:11551:16: error: invoking macro FX_FTYPE_FX ar gument 1: empty macro arguments are undefined)

	PR target/56445
	* config/avr/avr.c (avr_init_builtins): Use 'n' instead of empty
	macro parameters with: FX_FTYPE_FX, FX_FTYPE_FX_INT, INT_FTYPE_FX,
	INTX_FTYPE_FX, FX_FTYPE_INTX.
	* config/avr/builtins.def: Adjust respective DEF_BUILTIN.

From-SVN: r196332