Mark usage function as __dead2 in programs where it does not return

In most cases, usage does not return, so mark them as __dead2. For the
cases where they do return, they have not been marked __dead2.

Reviewed by: imp
Pull Request: https://github.com/freebsd/freebsd-src/pull/735

sbin/adjkerntz/adjkerntz.c

@@ -67,7 +67,7 @@ __FBSDID("$FreeBSD$");
 #define REPORT_PERIOD (30*60)
 
 static void fake(int);
-static void usage(void);
+static void usage(void) __dead2;
 
 static void
 fake(int unused __unused)

sbin/comcontrol/comcontrol.c

@@ -42,7 +42,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/types.h>
 #include <sys/ioctl.h>
 
-static void usage(void);
+static void usage(void) __dead2;
 
 static void
 usage(void)

sbin/fdisk/fdisk.c

@@ -258,7 +258,7 @@ static int decimal(const char *str, int *num, int deflt, uint32_t maxval);
 static int read_config(char *config_file);
 static void reset_boot(void);
 static int sanitize_partition(struct dos_partition *);
-static void usage(void);
+static void usage(void) __dead2;
 
 int
 main(int argc, char *argv[])

sbin/ldconfig/ldconfig.c

@@ -50,7 +50,7 @@
 #include "ldconfig.h"
 #include "rtld_paths.h"
 
-static void usage(void);
+static void usage(void) __dead2;
 
 int
 main(int argc, char **argv)

sbin/mdconfig/mdconfig.c

@@ -60,7 +60,7 @@ static struct md_ioctl mdio;
 static enum {UNSET, ATTACH, DETACH, RESIZE, LIST} action = UNSET;
 static int nflag;
 
-static void usage(void);
+static void usage(void) __dead2;
 static void md_set_file(const char *);
 static int md_find(const char *, const char *);
 static int md_query(const char *, const int, const char *);

sbin/newfs/newfs.c

@@ -124,7 +124,7 @@ static char	*disktype;
 
 static void getfssize(intmax_t *, const char *p, intmax_t, intmax_t);
 static struct disklabel *getdisklabel(void);
-static void usage(void);
+static void usage(void) __dead2;
 static int expand_number_int(const char *buf, int *num);
 
 ufs2_daddr_t part_ofs; /* partition offset in blocks, used with files */

sbin/newfs_msdos/newfs_msdos.c

@@ -51,7 +51,7 @@ static const char rcsid[] =
 
 static u_int argtou(const char *, u_int, u_int, const char *);
 static off_t argtooff(const char *, const char *);
-static void usage(void);
+static void usage(void) __dead2;
 
 static time_t
 get_tstamp(const char *b)

sbin/nos-tun/nos-tun.c

@@ -89,7 +89,7 @@ static struct ifreq ifrq;
 int net;                          /* socket descriptor */
 int tun;                          /* tunnel descriptor */
 
-static void usage(void);
+static void usage(void) __dead2;
 
 static int
 Set_address(char *addr, struct sockaddr_in *sin)

sbin/reboot/reboot.c

@@ -61,7 +61,7 @@ __FBSDID("$FreeBSD$");
 #include <unistd.h>
 #include <utmpx.h>
 
-static void usage(void);
+static void usage(void) __dead2;
 static u_int get_pageins(void);
 
 static int dohalt;

sbin/routed/rtquery/rtquery.c

@@ -131,7 +131,7 @@ static void query_loop(char *argv[], int) __attribute((__noreturn__));
 static int getnet(char *, struct netinfo *);
 static u_int std_mask(u_int);
 static int parse_quote(char **, const char *, char *, char *, int);
-static void usage(void);
+static void usage(void) __dead2;
 
 
 int

sbin/swapon/swapon.c

@@ -68,7 +68,7 @@ __FBSDID("$FreeBSD$");
 #include <string.h>
 #include <unistd.h>
 
-static void usage(void);
+static void usage(void) __dead2;
 static const char *swap_on_off(const char *, int, char *);
 static const char *swap_on_off_gbde(const char *, int);
 static const char *swap_on_off_geli(const char *, char *, int);

sbin/tunefs/tunefs.c

@@ -80,7 +80,7 @@ static char clrbuf[MAXBSIZE];
 static struct uufsd disk;
 #define	sblock disk.d_fs
 
-static void usage(void);
+static void usage(void) __dead2;
 static void printfs(void);
 static int journal_alloc(int64_t size);
 static void journal_clear(void);