configure.ac: Pull gio-unix dependency for all unix builds
configure.ac: Pull gio-unix dependency for all unix builds

It's now needed by gtk-launch, so it's just the case to enable it for all the
builds except the win32 one, instead of adding it for every unix backend.

https://bugzilla.gnome.org/show_bug.cgi?id=744086

Adamovskiy/gtk,alexlarsson/gtk,jadahl/gtk,jadahl/gtk,grubersjoe/adwaita,jigpu/gtk,grubersjoe/adwaita,jigpu/gtk,chergert/gtk,jadahl/gtk,jigpu/gtk,davidgumberg/gtk,jadahl/gtk,Adamovskiy/gtk,chergert/gtk,davidgumberg/gtk,Adamovskiy/gtk,Adamovskiy/gtk,jadahl/gtk,grubersjoe/adwaita,grubersjoe/adwaita,davidgumberg/gtk,chergert/gtk,Adamovskiy/gtk,alexlarsson/gtk,Adamovskiy/gtk,jadahl/gtk,alexlarsson/gtk,chergert/gtk,davidgumberg/gtk,chergert/gtk,Adamovskiy/gtk,chergert/gtk,jigpu/gtk,davidgumberg/gtk,alexlarsson/gtk,davidgumberg/gtk,grubersjoe/adwaita,grubersjoe/adwaita,jigpu/gtk,jigpu/gtk,grubersjoe/adwaita,jigpu/gtk,alexlarsson/gtk,jadahl/gtk,davidgumberg/gtk,chergert/gtk,alexlarsson/gtk,davidgumberg/gtk,alexlarsson/gtk,grubersjoe/adwaita,Adamovskiy/gtk,jadahl/gtk,jigpu/gtk,alexlarsson/gtk,chergert/gtk