>>char rcsid[] __attribute__ ((unused)) = "...";

Rather than taint all code with non-portable constructs
how about a script, say, "checkcc" with something like

	cc -warnings -more-warnings $* 2>&1 | \
	    egrep -v ": warning: `(rcsid|sccsid)' declared but not used$" |
	    grep -v ": warning: any other annoying warnings here$'

then simply "make CC=checkcc all".
									++sja