tests/execveat.c: use libtests

* tests/execveat.c: Use SKIP_MAIN_UNDEFINED.
diff --git a/tests/execveat.c b/tests/execveat.c
index e268d87..af3d08e 100644
--- a/tests/execveat.c
+++ b/tests/execveat.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015 Dmitry V. Levin <ldv@altlinux.org>
+ * Copyright (c) 2015-2016 Dmitry V. Levin <ldv@altlinux.org>
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -46,10 +46,6 @@
 
 #else
 
-int
-main(void)
-{
-	return 77;
-}
+SKIP_MAIN_UNDEFINED("__NR_execveat")
 
 #endif