fix building in GNU/kFreeBSD

[mones]

Hi,

Building in GNU/kFreeBSD architectures currently fails. Inspired by the existing trick I'm applying the following patch in the Debian package build to fix that issue, but would be better if included in your code:

https://salsa.debian.org/debian/ttyload/-/blob/master/debian/patches/11-gnu-kfreebsd-compile.patch

It's a very simple patch, but If you prefer a pull request, please let me know.

best regards,