Since Tor does not currently provide win32 binaries for json-glib we
need to cross compile it before we can build clutter. This extends
mingw-fetch-dependencies.sh so it can fetch, unpack and cross-compile
json-glib into the same prefix as the binary dependencies.
It shouldn't be necessary to explicitly override CC,CPP,AR,NM,LD etc in
the env.sh helper script that mingw-fetch-dependencies.sh generates.
Clutter's ./configure script should figure all of those out for us.
This removes the "Do you want to checkout and build Clutter?" option
from the mingw-cross-compile.sh script and renames the script
mingw-fetch-dependencies.sh
As it stands the mingw-cross-compile.sh script isn't enough to fetch all
the dependencies for building clutter, since Tor doesn't provide binaries
for json-glib so the option to checkout and build clutter can't work.
Also it doesn't seem ideal to clone a fresh clutter repo instead of
being able to compile the source of the current repo.
