Add cross file for windows builds
This is a preliminary file that adds support for building gradio for windows on linux.
This was built using the mingw64 packages in fedora plus the mingw64 json copr package.
I also had to procure executables that provided the proper dlls for running gradio.
- https://gstreamer.freedesktop.org/
- https://github.com/tschoonj/GTK-for-Windows-Runtime-Environment-Installer
I also needed to compile a gschema file on the linux machine and transfer it over to windows.