pango: run pango-querymodules on the target instead of on the host

pango: run pango-querymodules on the target instead of on the host

We needed to build pango for the host in order to compile
pango-querymodules for the host, which was used to produce
/etc/pango/pango.modules. Unfortunately:

 * This produces an incorrect /etc/pango/pango.modules (no modules
   detected in my case), probably because the host pango-querymodules
   was looking at host pango modules

 * This requires to build pango for the host, which requires to build
   cairo for the host, which requires to build X11 for the host.

To make things work and remove the dependency between pango and
host-pango, we introduce a S25pango script that creates
/etc/pango/pango.modules on startup if it doesn't exist, just as we do
with libgtk2 for /etc/gtk-2.0/gdk-pixbuf.loaders.

Since host-pango is no longer needed, we remove all definitions
related to it.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>