Test on a variety of different OSes

[nightlark]

Some additional platforms to test:

• iOS
• Android
• Any interesting OS available on the GCC compile farm

[nightlark]

https://man.sr.ht/builds.sr.ht/compatibility.md -- sourcehut could be a decent option for testing a wide variety of different OSes (BSDs, Guix, NixOS), potentially on several architectures (or use qemu).