updates tailcale/corp#22371
Adds custom macOS vm tooling. See the README for
the general gist, but this will spin up VMs with unixgram
capable network interfaces listening to a named socket,
and with a virtio socket device for host-guest communication.
We can add other devices like consoles, serial, etc as needed.
The whole things is buildable with a single make command, and
everything is controllable via the command line using the TailMac
utility.
This should all be generally functional but takes a few shortcuts
with error handling and the like. The virtio socket device support
has not been tested and may require some refinement.
Signed-off-by: Jonathan Nobels <jonathan@tailscale.com>
