Fix build after r326554; reconnect sponge to build again.

usr.bin/Makefile

@@ -148,6 +148,7 @@ SUBDIR=	alias \
 	soelim \
 	sort \
 	split \
+	sponge \
 	stat \
 	stdbuf \
 	strings \

usr.bin/sponge/sponge.c

@@ -172,7 +172,8 @@ main(int argc, char* argv[])
 	bufremain = bufcnt;
 
 	while (bufremain > 0) {
-		whichbuf = (bufremain < maxiovec) ? bufremain : maxiovec;
+		whichbuf = bufremain < (unsigned long) maxiovec
+			? bufremain : maxiovec;
 		bufremain -= whichbuf;
 
 		i = writev(fd, iov, whichbuf);