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

usr.bin/mesg/mesg.c

@@ -57,7 +57,7 @@ __FBSDID("$FreeBSD$");
 #include <string.h>
 #include <unistd.h>
 
-static void usage(void);
+static void usage(void) __dead2;
 
 int
 main(int argc, char *argv[])

usr.bin/mkfifo/mkfifo.c

@@ -56,7 +56,7 @@ __FBSDID("$FreeBSD$");
 #define	BASEMODE	S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | \
 			S_IROTH | S_IWOTH
 
-static void usage(void);
+static void usage(void) __dead2;
 
 static int f_mode;
 

usr.bin/mktemp/mktemp.c

@@ -50,7 +50,7 @@ static const char rcsid[] =
 	"$FreeBSD$";
 #endif /* not lint */
 
-static void usage(void);
+static void usage(void) __dead2;
 
 static const struct option long_opts[] = {
 	{"directory",	no_argument,	NULL,	'd'},

usr.bin/mkuzip/mkuzip.c

@@ -99,7 +99,7 @@ static const struct mkuz_format uzip_fmts[] = {
 };
 
 static struct mkuz_blk *readblock(int, u_int32_t);
-static void usage(void);
+static void usage(void) __dead2;
 static void cleanup(void);
 
 static char *cleanfile = NULL;

usr.bin/mt/mt.c

@@ -180,7 +180,7 @@ static const struct commands {
 static const char *getblksiz(int);
 static void printreg(const char *, u_int, const char *);
 static void status(struct mtget *);
-static void usage(void);
+static void usage(void) __dead2;
 const char *get_driver_state_str(int dsreg);
 static void st_status (struct mtget *);
 static int mt_locate(int argc, char **argv, int mtfd, const char *tape);

usr.bin/netstat/main.c

@@ -192,7 +192,7 @@ static struct protox *protoprotox[] = {
 					 NULL };
 
 static void printproto(struct protox *, const char *, bool *);
-static void usage(void);
+static void usage(void) __dead2;
 static struct protox *name2protox(const char *);
 static struct protox *knownname(const char *);
 

usr.bin/newkey/newkey.c

@@ -90,7 +90,7 @@ static char PKFILE[] = "/etc/publickey";
 static const char *err_string(int);
 #endif	/* YP */
 
-static void usage(void);
+static void usage(void) __dead2;
 
 int
 main(int argc, char *argv[])

usr.bin/nfsstat/nfsstat.c

@@ -109,7 +109,7 @@ static int extra_output = 0;
 
 static void intpr(int, int);
 static void printhdr(int, int, int);
-static void usage(void);
+static void usage(void) __dead2;
 static char *sperc1(int, int);
 static char *sperc2(int, int);
 static void exp_intpr(int, int, int);

usr.bin/nohup/nohup.c

@@ -56,7 +56,7 @@ __FBSDID("$FreeBSD$");
 #include <unistd.h>
 
 static void dofile(void);
-static void usage(void);
+static void usage(void) __dead2;
 
 #define	FILENAME	"nohup.out"
 /*

usr.bin/paste/paste.c

@@ -65,7 +65,7 @@ static int delimcnt;
 static int parallel(char **);
 static int sequential(char **);
 static int tr(wchar_t *);
-static void usage(void);
+static void usage(void) __dead2;
 
 static wchar_t tab[] = L"\t";
 

usr.bin/perror/perror.c

@@ -37,7 +37,7 @@ __FBSDID("$FreeBSD$");
 #include <locale.h>
 #include <sys/errno.h>
 
-static void usage(void);
+static void usage(void) __dead2;
 
 int 
 main(int argc, char **argv)

usr.bin/quota/quota.c

@@ -86,7 +86,7 @@ struct quotause {
 
 static char *timeprt(int64_t seconds);
 static struct quotause *getprivs(long id, int quotatype);
-static void usage(void);
+static void usage(void) __dead2;
 static int showuid(u_long uid);
 static int showgid(u_long gid);
 static int showusrname(char *name);

usr.bin/random/random.c

@@ -61,7 +61,7 @@ __FBSDID("$FreeBSD$");
 
 #include "randomize_fd.h"
 
-static void usage(void);
+static void usage(void) __dead2;
 
 int
 main(int argc, char *argv[])

usr.bin/rev/rev.c

@@ -55,7 +55,7 @@ __FBSDID("$FreeBSD$");
 #include <unistd.h>
 #include <wchar.h>
 
-static void usage(void);
+static void usage(void) __dead2;
 
 int
 main(int argc, char *argv[])

usr.bin/rpcgen/rpc_main.c

@@ -64,7 +64,7 @@ static void clnt_output(const char *, const char *, int, const char * );
 static char *generate_guard(const char *);
 static void c_initialize(void);
 
-static void usage(void);
+static void usage(void) __dead2;
 static void options_usage(void);
 static int do_registers(int, const char **);
 static int parseargs(int, const char **, struct commandline *);

usr.bin/rwall/rwall.c

@@ -71,7 +71,7 @@ static char *mbuf;
 static char notty[] = "no tty";
 
 static void	makemsg(const char *);
-static void usage(void);
+static void usage(void) __dead2;
 
 /* ARGSUSED */
 int

usr.bin/rwho/rwho.c

@@ -83,7 +83,7 @@ static struct	myutmp {
 static time_t	now;
 static int	aflg;
 
-static void usage(void);
+static void usage(void) __dead2;
 static int utmpcmp(const void *, const void *);
 
 int