*: remove a few more cases of argc usage. -89 bytes.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

libbb/Kbuild

@@ -92,6 +92,7 @@ lib-y += setup_environment.o
 lib-y += sha1.o
 lib-y += signals.o
 lib-y += simplify_path.o
+lib-y += single_argv.o
 lib-y += skip_whitespace.o
 lib-y += speed_table.o
 lib-y += str_tolower.o

libbb/single_argv.c

@@ -0,0 +1,16 @@
+/* vi: set sw=4 ts=4: */
+/*
+ * Utility routines.
+ *
+ * Copyright (C) 2009 Denys Vlasenko
+ *
+ * Licensed under GPLv2, see file LICENSE in this tarball for details.
+ */
+#include "libbb.h"
+
+char* FAST_FUNC single_argv(char **argv)
+{
+	if (!argv[1] || argv[2])
+		bb_show_usage();
+	return argv[1];
+}