mac OS build using darling

[PeterSurda]

Darling is an implementation of macOS system interfaces on linux, similarly like wine is an implementation of Windows system on linux. Based on my research there is a good chance building macOS binaries of PyBitmessage using Darling will work, i.e. produce binaries that will work on macOS. The environment appears to be compatible with macOS 10.15 Catalina, and xcode command line tools 12.4. Unfortunately there is some work left on python2 and Qt4 compatibility which prevents the build from progressing, so I got stuck. I made a fork of qt4 and python2 casks so we can make patched versions until a python3 / Qt5 port is working.

Once a build procedure is available, it can be plugged into the existing build system by running on a ubuntu VM. I don't think it will work in docker as it needs a special kernel module, which isn't very stable, running it in a VM is the official recommended process of the darling project.

A lack of mac OS binary is preventing a new release, so it would be nice if this was solved.