With these changes I'm able to cross-build pForth using MinGW:
make -f build/unix/Makefile SRCDIR=. CC=/usr/pkg/cross/bin/i386--mingw32-cc IO_SOURCE=pf_io_win32_console.c pforth
or
make -f build/unix/Makefile SRCDIR=. CC=/usr/pkg/cross/bin/i386--mingw32-cc IO_SOURCE=pf_io_win32.c pforth
One can use dictionary file built for the same platform under another operating system.
It is possible to extend support to build dictionary file,
but I don't know how to cross-build 32-bit dictionary on 64-bit system yet.