Make Briar Desktop work on macOS (x86/ARM?)

Similar to #31, we also want Briar Desktop to run on macOS. While for Windows and Linux we modified our own tor-reproducer to build tor binaries, for macOS support we could try using the official toolchain from Tor.

See the respective issue Create a new build target to package tor daemon, pluggable transports and dependencies and my forum thread Are there any official reproducible tor/obfs4proxy binaries?