Add compatibility build mode

[Kobzol]

It would be nice to have a build mode (probably using a --feature or perhaps a --cfg) that would ignore Linux-specific features that can prevent HQ from compiling on non-Linux OSes (macOS/Windows). We should also test this mode on CI on macOS and Windows.

Trying out HQ locally is a quite important feature, even if we don't support running HQ in production environments on non-Linux platforms.