[Bug c++/109988] -iwithprefix doesn't add folder to end of search list

[ivan.lazaric.gcc at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109988

--- Comment #1 from Ivan Lazaric <ivan.lazaric.gcc at gmail dot com> ---
In `gcc/c-family/c-opts.cc`:
```
    case OPT_iwithprefix:
      add_prefixed_path (arg, INC_SYSTEM);
      break;
```

Should `INC_SYSTEM` actually be `INC_AFTER` ?