dump-vtable.c: 2 * undefined behaviour ?

1.

dump-vtable.c:315:46: warning: flag '0' results in undefined behavior with 'p' conversion specifier [-Wformat]

```
 printf("(int (*)(...)) -%016p\n", (void*) -(ptrdiff_t)vfuncp);
```

2.

dump-vtable.c:319:45: warning: flag '0' results in undefined behavior with 'p' conversion specifier [-Wformat]

```
  printf("(int (*)(...)) %016p\n", vfuncp);
```
