Add Cross.toml to allow easy cross-building

[srd424]

This allows easy cross-building / cross-compiling using https://github.com/cross-rs/cross.

[srd424]

Though it would help if the cross-rs docker images had a reasonably up-to-date libavformat :(

[izderadicka]

@srd424 I do not know cross.rs. Concerning libavformat I keep prebuild bindgen bindings for several major past versions to keep building simpler. Oldest is from ffmpeg 4.3. I did not find any notable benefit(from perspective of audioserve) in newer version - 5 and 6. If there is any problem with supported versions of libavformat pls let me know.

And thank you for PR.

[srd424]

Ah, I'll have to look at the bindgen stuff, I'm not very familiar with the rust ecosystem - let alone the actual language! At the moment I have my hand-crafted arm64 build environment, I was hoping to be able to dump it and use cross-rs, but looks like I need to do a little more work. According to docs I should be able to create a custom cross-rs-compatible build image quite easily so that's perhaps the easiest compromise.