Mark functions not returning as sudo_noreturn

We also put NOTREACHED where it applies.

plugins/sudoers/testsudoers.c

@@ -201,7 +201,7 @@ main(int argc, char *argv[])
 		break;
 	    default:
 		usage();
-		break;
+	    /* NOTREACHED */
 	}
     }
     argc -= optind;
@@ -731,7 +731,7 @@ testsudoers_error(const char *buf)
     return fputs(buf, stderr);
 }
 
-static void
+sudo_noreturn static void
 usage(void)
 {
     (void) fprintf(stderr, "usage: %s [-dt] [-G sudoers_gid] [-g group] [-h host] [-i input_format] [-P grfile] [-p pwfile] [-U sudoers_uid] [-u user] <user> <command> [args]\n", getprogname());