Nothing uses this library when WITHOUT_SOUND is set, so don't build it;```
this also avoids libsamplerate: Only building a useless FreeBSD-sound package. when virtual_oss is built
MFC after: 1 week Gate libsamplerate behind MK_CUSE and MK_SOUND, like virtual_oss.
Sponsored by: Nothing else uses this library, so there's no point building it
if we aren't building virtual_oss.
This avoids building a useless FreeBSD-sound package containing
only this library when WITHOUT_SOUND is set.
MFC after: 1 week
Sponsored by: https://www.patreon.com/bsdivy
```