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/asa/asa.c

@@ -47,7 +47,7 @@ __FBSDID("$FreeBSD$");
 #include <unistd.h>
 
 static void asa(FILE *);
-static void usage(void);
+static void usage(void) __dead2;
 
 int
 main(int argc, char *argv[])

usr.bin/banner/banner.c

@@ -1026,7 +1026,7 @@ static char	print[DWIDTH];
 static int	debug, i, j, linen, max, nchars, pc, term, trace, x, y;
 static int	width = DWIDTH;	/* -w option: scrunch letters to 80 columns */
 
-static void usage(void);
+static void usage(void) __dead2;
 
 int
 main(int argc, char *argv[])

usr.bin/biff/biff.c

@@ -51,7 +51,7 @@ __FBSDID("$FreeBSD$");
 #include <stdlib.h>
 #include <unistd.h>
 
-static void usage(void);
+static void usage(void) __dead2;
 
 int
 main(int argc, char *argv[])

usr.bin/bintrans/uuencode.c

@@ -70,7 +70,7 @@ extern int main_base64_encode(const char *, const char *);
 static void encode(void);
 static void base64_encode(void);
 static int arg_to_col(const char *);
-static void usage(void);
+static void usage(void) __dead2;
 
 static FILE *output;
 static int mode;

usr.bin/brandelf/brandelf.c

@@ -52,7 +52,7 @@ __FBSDID("$FreeBSD$");
 static int elftype(const char *);
 static const char *iselftype(int);
 static void printelftypes(void);
-static void usage(void);
+static void usage(void) __dead2;
 
 struct ELFtypes {
 	const char *str;

usr.bin/c99/c99.c

@@ -50,7 +50,7 @@ static u_int cargs, nargs;
 
 static void addarg(const char *);
 static void addlib(const char *);
-static void usage(void);
+static void usage(void) __dead2;
 
 int
 main(int argc, char *argv[])

usr.bin/chat/chat.c

@@ -145,7 +145,7 @@ static int say_next, hup_next;
 
 void *dup_mem(void *b, size_t c);
 void *copy_of(char *s);
-static void usage(void);
+static void usage(void) __dead2;
 void chat_logf(const char *fmt, ...);
 void fatal(int code, const char *fmt, ...);
 SIGTYPE sigalrm(int signo);

usr.bin/chkey/chkey.c

@@ -74,7 +74,7 @@ static char PKFILE[] = "/etc/publickey";
 #endif	/* YP */
 static char ROOTKEY[] = "/etc/.rootkey";
 
-static void usage(void);
+static void usage(void) __dead2;
 extern int yp_update(char *, char *, int, char *, size_t, char *, size_t);
 
 int

usr.bin/cksum/cksum.c

@@ -58,7 +58,7 @@ __FBSDID("$FreeBSD$");
 
 #include "extern.h"
 
-static void usage(void);
+static void usage(void) __dead2;
 
 int
 main(int argc, char **argv)

usr.bin/cmp/cmp.c

@@ -86,7 +86,7 @@ siginfo(int signo)
 }
 #endif
 
-static void usage(void);
+static void usage(void) __dead2;
 
 static bool
 parse_iskipspec(char *spec, off_t *skip1, off_t *skip2)

usr.bin/colrm/colrm.c

@@ -58,7 +58,7 @@ __FBSDID("$FreeBSD$");
 #define	TAB	8
 
 void check(FILE *);
-static void usage(void);
+static void usage(void) __dead2;
 
 int
 main(int argc, char *argv[])

usr.bin/cpuset/cpuset.c

@@ -69,7 +69,7 @@ static id_t id;
 static cpulevel_t level;
 static cpuwhich_t which;
 
-static void usage(void);
+static void usage(void) __dead2;
 
 struct numa_policy {
 	const char 	*name;

usr.bin/ctags/ctags.c

@@ -87,7 +87,7 @@ char	lbuf[LINE_MAX];
 
 void	init(void);
 void	find_entries(char *);
-static void usage(void);
+static void usage(void) __dead2;
 
 int
 main(int argc, char **argv)