OCC no longer fails on unknown flag

OrangeC 7.10.59 silently accepts an unknown compiler flag:

```console
>occ -c example.c -BadFlag && echo Success || echo Failure
occ (OrangeC) Version 7.10.59
...
Unknown switch '-B'
...
Success
```

OrangeC 7.0.7 rejected them:

```console
>occ -c example.c -BadFlag && echo Success || echo Failure
occ (OrangeC) Version 7.0.7
...
Unknown switch '-B'
...
Failure
```
