Generate fake font cache for compressed fonts
If language specific font is needed, but it was bundled without compression, it occupy extra "N" MiB. As a workaround, it might be better to use compressed font, but fc-cache doesn't support such a compressed font format.
Thus generate fake font cache in advance during building netboot-gtk image, then it will be used by gtk-font-set from GUI installer.
See https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1037256