Fix 128_run_atexit.c on linux

if we include standard headers on glibc-based systems then
we can't use '__attribute__' (those are defined away for unknown
compilers) but must use '__attribute' (or #undef that token).

tests/tests2/128_run_atexit.c

@@ -25,7 +25,7 @@ void cleanup4(int ret, void *arg)
     printf ("%d %s\n", ret, (char *) arg);
 }
 
-void __attribute__((destructor)) cleanup5(void)
+void __attribute((destructor)) cleanup5(void)
 {
     printf ("cleanup5\n");
 }