gm2 -g -fmake-I=. -flibs=pim-coroutine -fmakeall -lncurses -lpth testwin.mod
ok you need to install libpth-dev,
$ sudo apt-get install libpth-dev
I also tried
./Makefile.in post-install
This also failed saying lots of commands were not found like srcdir,
gm2dir, all, @echo, XGM2, etc
ok to build examples from a Makefile.in you need to move to the
equivalent build directory and type 'make'. The program 'configure'
will have created a 'Makefile' from the src 'Makefile.in' and
instantiated values based on your system ($srcdir, $prefix etc).
$ cd<build-dir>/gcc/gm2/examples/ncurses
$ make post-install
where<build-dir> is the root directory of your gm2 build tree. It
assumes you have built gm2 from source (and the 'configure' command is
done right at the beginning of the complete compiler build).