libselinux/utils: add noreturn attribute to selinux_check_access's usage

When building libselinux, clang reports the following warning:

    selinux_check_access.c:8:1: error: function 'usage' could be
    declared with attribute 'noreturn' [-Werror,-Wmissing-noreturn]

While at it, make progname const.

Signed-off-by: Nicolas Iooss <nicolas.iooss@m4x.org>

libselinux/utils/selinux_check_access.c

@@ -4,7 +4,7 @@
 #include <unistd.h>
 #include <selinux/selinux.h>
 
-static void usage(char *progname)
+static __attribute__ ((__noreturn__)) void usage(const char *progname)
 {
 	fprintf(stderr, "usage:  %s [-a auditdata] scon tcon class perm\n"
 		"\nWhere:\n\t"