As far as i know, MAN-AT-ARMS applied all 1.42d changes to iortcw and rtcwcoop a year ago, or so. I remember that some years ago, when fretn released the first version of his rtcwcoop code, without any compiled binaries, there where a VC project included, but recently there isn't one.
I for myself are no programmer, and my understanding of code is extremely rudimentary, so unfortunately i can't help you with this.
But why you can't work in Cygwin? You just need it to compile the code. You can create a "fake project" to work with the code, and use Cygwin to compile. I used the same approach, i created a "fake project" in XCode to change the code, and compiled in the terminal, using the shell script.
If i have some free time, i will try to compile the code for Linux and Windows aswell, just to be sure. ;-)
When i tested my build i can do a fork of iortcw, if you want, and you can base your codework on this. This way RealRTCW would grow cross platform. And you could incorporate fixes and features inherited from ioQuake3/ioRTCW.
I am not programmer as well. "Hello world" is the best thing I ever wrote.
Anyway, I was trying to work with Cygwin for a couple times, but it didn't worked out. So I abandoned this.
Unfortunately, right now I don't have much time to work on my mod. I can barely find some time to work on 2.1 version. So probably this will stay as it is now.