So I gave this a quick try and it did of course become a rabbithole - but mainly caused by my own Windows configs.
- I tried it on the main PC and then remembered it did not have Cygwin, just MSYS2 (mostly the same thing but slightly less damage) and I don't really want to install Cygwin there...
- I tried it on the old PC with other Atari stuff on it and where Cygwin32 is working - an old XP machine and air-gapped (!) - and it seems to mostly work. I say 'mostly' because the makefile is for some reason trying to use BC which is a commandline calculator. No idea why but it is, and I don't have it installed in that old Cygwin. And since it is an air-gapped machine, I'll not be installing that anytime soon
I was using the command
> make clean
...then
> make TOSVERSION=206 COUNTRY=uk
Running the
second make command a second time however dodged the BC missing command error (it must be used at a one-time configure step, not a build step so the error only happens once) and left me with a new error, a missing localcfg.h. That's just full of definitions for TOS206, MEDUSA and so on so I just cloned & renamed the patchdef.h include as it has the same stuff in it and a comment about making your own localcfg.h.
On 3rd attempt, it spent a decent amount of time compiling all the files - then failed to link with a bizarre syntax error. I'll put that down to either (1) ancient Cygwin32 or (2) the failed configure step at the beginning due to the missing BC calculator tool.
Last - the patch I sent you was meant to
replace some existing lines at the top of
Makefile.cmn, not lines to add to
Makefile. Sorry, I didn't explain that well (or at all) but it was kinda late at the time.

that's the only change I made - the rest looks like issues with my old machine config...