Homebrew on Apple Silicon / XCode 13.2 support

[jgavris]

• Supports detecting brew --prefix for the new /opt/homebrew home on Apple Silicon.
• Fixes shared_ptr cast warning in RMateServer.
• vfork is now deprecated (has same behavior as fork on macOS 12 and above, and will be removed eventually).

[hovsater]

@sorbits would it be possible to give this a look? Would really appreciate being able to build TextMate on my Mac again. 🙂

[faisal]

@sorbits do you expect to do something with this?

[garsaud]

It seems that this repo is dead. Last commit is from 2021-10-12…