[Bug ipa/117796] Accepting undefined symbols with -flto -O0 -ftoplevel-reorder -fipa-reference-addressable

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117796

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
The correct way of fixing this is doing the following:
```
   char some_unavailable_symbol();
   char (*f)() __attribute__((used));

   int main() {
        f = some_unavailable_symbol;
        return 0;
   }
```

That is marking f as being used.