Fix linking on FreeBSD

Summary:
Linking fails with (see T8802)
```
12:25:27 /usr/bin/ld: error: unable to find library -lfreecell-solver
```

Reviewers: #freebsd, fabiank, #kde_games

Reviewed By: fabiank

Subscribers: kde-games-devel

Differential Revision: https://phabricator.kde.org/D13057