gst-libav-1.0.recipe: Fix configure on Windows
gst-libav-1.0.recipe: Fix configure on Windows

Needs extra quoting for extra config arguments passed to ffmpeg that
have spaces in them.

https://bugzilla.gnome.org/show_bug.cgi?id=796511

centricular/cerbero,nirbheek/cerbero,centricular/cerbero,GStreamer/cerbero,centricular/cerbero,fluendo/cerbero,GStreamer/cerbero,atsushieno/cerbero,atsushieno/cerbero,atsushieno/cerbero,GStreamer/cerbero,nirbheek/cerbero,atsushieno/cerbero,fluendo/cerbero,nirbheek/cerbero,centricular/cerbero,GStreamer/cerbero,GStreamer/cerbero,fluendo/cerbero,centricular/cerbero,atsushieno/cerbero,fluendo/cerbero,fluendo/cerbero,nirbheek/cerbero