Revert "Do not use arg.h for tools which take no flags"

This reverts commit 9016d288f1.

Tools that have no options are required by POSIX to support "--" so
that conforming applications have a way to shield their operands from
implementations that provide options as an extension.

echo(1) is just an exception, so it is handled specially.

See OPTIONS in https://pubs.opengroup.org/onlinepubs/9699919799.2018edition/utilities/V3_chap01.html#tag_17_04

chroot.c

@@ -17,7 +17,10 @@ main(int argc, char *argv[])
 	char *shell[] = { "/bin/sh", "-i", NULL }, *aux, *cmd;
 	int savederrno;
 
-	argv0 = *argv, argv0 ? (argc--, argv++) : (void *)0;
+	ARGBEGIN {
+	default:
+		usage();
+	} ARGEND
 
 	if (!argc)
 		usage();

cksum.c

@@ -92,12 +92,21 @@ cksum(int fd, const char *s)
 	putchar('\n');
 }
 
+static void
+usage(void)
+{
+	eprintf("usage: %s [file ...]\n", argv0);
+}
+
 int
 main(int argc, char *argv[])
 {
 	int fd;
 
-	argv0 = *argv, argv0 ? (argc--, argv++) : (void *)0;
+	ARGBEGIN {
+	default:
+		usage();
+	} ARGEND
 
 	if (!argc) {
 		cksum(0, NULL);

hostname.c

@@ -16,7 +16,10 @@ main(int argc, char *argv[])
 {
 	char host[HOST_NAME_MAX + 1];
 
-	argv0 = *argv, argv0 ? (argc--, argv++) : (void *)0;
+	ARGBEGIN {
+	default:
+		usage();
+	} ARGEND
 
 	if (!argc) {
 		if (gethostname(host, sizeof(host)) < 0)

link.c

@@ -12,7 +12,10 @@ usage(void)
 int
 main(int argc, char *argv[])
 {
-	argv0 = *argv, argv0 ? (argc--, argv++) : (void *)0;
+	ARGBEGIN {
+	default:
+		usage();
+	} ARGEND
 
 	if (argc != 2)
 		usage();

nohup.c

@@ -19,7 +19,10 @@ main(int argc, char *argv[])
 {
 	int fd, savederrno;
 
-	argv0 = *argv, argv0 ? (argc--, argv++) : (void *)0;
+	ARGBEGIN {
+	default:
+		usage();
+	} ARGEND
 
 	if (!argc)
 		usage();

printenv.c

@@ -6,13 +6,22 @@
 
 extern char **environ;
 
+static void
+usage(void)
+{
+	eprintf("usage: %s [var ...]\n", argv0);
+}
+
 int
 main(int argc, char *argv[])
 {
 	char *var;
 	int ret = 0;
 
-	argv0 = *argv, argv0 ? (argc--, argv++) : (void *)0;
+	ARGBEGIN {
+	default:
+		usage();
+	} ARGEND
 
 	if (!argc) {
 		for (; *environ; environ++)

setsid.c

@@ -15,7 +15,10 @@ main(int argc, char *argv[])
 {
 	int savederrno;
 
-	argv0 = *argv, argv0 ? (argc--, argv++) : (void *)0;
+	ARGBEGIN {
+	default:
+		usage();
+	} ARGEND
 
 	if (!argc)
 		usage();

sleep.c

@@ -14,7 +14,10 @@ main(int argc, char *argv[])
 {
 	unsigned seconds;
 
-	argv0 = *argv, argv0 ? (argc--, argv++) : (void *)0;
+	ARGBEGIN {
+	default:
+		usage();
+	} ARGEND
 
 	if (argc != 1)
 		usage();

sponge.c

@@ -17,7 +17,10 @@ main(int argc, char *argv[])
 	char tmp[] = "/tmp/sponge-XXXXXX";
 	int fd, tmpfd;
 
-	argv0 = *argv, argv0 ? (argc--, argv++) : (void *)0;
+	ARGBEGIN {
+	default:
+		usage();
+	} ARGEND
 
 	if (argc != 1)
 		usage();

sync.c

@@ -12,7 +12,10 @@ usage(void)
 int
 main(int argc, char *argv[])
 {
-	argv0 = *argv, argv0 ? (argc--, argv++) : (void *)0;
+	ARGBEGIN {
+	default:
+		usage();
+	} ARGEND
 
 	if (argc)
 		usage();

tty.c

@@ -15,7 +15,10 @@ main(int argc, char *argv[])
 {
 	char *tty;
 
-	argv0 = *argv, argv0 ? (argc--, argv++) : (void *)0;
+	ARGBEGIN {
+	default:
+		usage();
+	} ARGEND
 
 	if (argc)
 		usage();

unlink.c

@@ -12,7 +12,10 @@ usage(void)
 int
 main(int argc, char *argv[])
 {
-	argv0 = *argv, argv0 ? (argc--, argv++) : (void *)0;
+	ARGBEGIN {
+	default:
+		usage();
+	} ARGEND
 
 	if (argc != 1)
 		usage();

yes.c

@@ -3,12 +3,21 @@
 
 #include "util.h"
 
+static void
+usage(void)
+{
+	eprintf("usage: %s [string ...]\n", argv0);
+}
+
 int
 main(int argc, char *argv[])
 {
 	char **p;
 
-	argv0 = *argv, argv0 ? (argc--, argv++) : (void *)0;
+	ARGBEGIN {
+	default:
+		usage();
+	} ARGEND
 
 	for (p = argv; ; p = (*p && *(p + 1)) ? p + 1 : argv) {
 		fputs(*p ? *p : "y", stdout);