Windows support

[Gia Hung Nguyen]

>From Google Groups they told it should build on Cygwin. I tried on Cygwin but 
>it failed.

The repository the document used is now invalid: 
https://www.nongnu.org/gm2/11/building_on_gcc_11.html

This mailing list discussion addressed it: 
https://lists.gnu.org/archive/html/gm2/2022-07/msg00008.html

But it's not really, the repo at http://floppsie.comp.glam.ac.uk/git/gm2 is 
very unstable, it will stuck at 48% when cloning.

So everyone, we will clone from gcc's github mirror, the branch devel/modula-2:

git clone -b devel/modula-2 https://github.com/gcc-mirror/gcc gm2-floppsie

The configuration process is successfull but the actual building failed with no 
rules for target!

BTW, I don't think Cygwin should be needed. GM2 should be built out of the box 
on MSYS2 MINGW64 (targets native Win32, no linking with cygwin-1.dll or 
msys-2.0.dll).

Please have a look: https://github.com/brechtsanders/winlibs_mingw/issues/110

If you could get it built with MINGW64 he would happily build and ship it with 
his MINGW64 distribution.