vdev/audio: CPAL on Linux with ALSA host hangs

[obiwac]

I'm running into this pretty weird issue with the audio VDEVs on Linux, where the data callback in build_output_stream() is never called, because the stream worker thread spawned by this blocks on the following line in src/host/alsa/mod.rs in CPAL:

let res = alsa::poll::poll(descriptors, *poll_timeout)?;

This seems to only happen in the VDEV though. On platforms with this issue, running examples/beep.rs for example works perfectly fine. So I'm suspecting this maybe has something to do with running in dynamically loaded code, though I really have no idea what that something could be exactly at the moment.

CPAL on FreeBSD doesn't exhibit this issues whatsoever.

This leads to the question: should we just use cubeb instead? Super cross-platform, mature, and had Rust bindings too anyways.

[obiwac]

I'm working on a new experimental backend using cubeb instead of CPAL, and hopefully that'll make this guy irrelevant once I replace the current audio VDEV with that implementation.