make-ring: now able to build Ring for Windows

The script is modified so we can compile Ring for
Windows by using '--distribution=mingw[32|64]'. At the moment, it
can only be used on Fedora (>=23).

Modifications:
 * script/win_compile.sh do the actual job
 * make-ring.py call this script when needed

Change-Id: I964b2bb9fb174bebd8e6b8746f3721066c278251
Reviewed-by: Guillaume Roguez <guillaume.roguez@savoirfairelinux.com>