Sorry to hear the trouble you had to go through. Two quick comments:
1) There is actually no need to recompile osFWUpdater — it’s just a GUI for running avrdude command. You can directly run command ‘avrdude -c arduino -p m1284p -P /dev/ttyxxx -U flash:w:xxx.hex’ where /dev/ttyxxx is the serial port name, and xxx.hex is the firmware file name.
2) I am also a bit surprised that VirtualBox in Mac doesn’t work — you should be able to pass the USB device through to the virtual system, and therefore it should be fine even if the host system doesn’t have the driver for that USB device. To do so you will need to go to the VirtualBox menu -> USB devices and select the ch340g device so that it can be passed through to the virtual system.