Fix warnings and set WARNS to 6.

MFC after:	1 week

tools/tools/aac/Makefile

@@ -2,6 +2,7 @@
 
 PROG=	aac_checkq
 NO_MAN=
+WARNS?=6
 BINDIR?=/usr/local/bin
 
 .include <bsd.prog.mk>

tools/tools/aac/aac_checkq.c

@@ -34,7 +34,11 @@ __FBSDID("$FreeBSD$");
 #include <errno.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 #include <strings.h>
+#include <unistd.h>
+
+void usage(void);
 
 /*
  * Simple program to print out the queue stats on the given queue index.