tools: generate pkg-config files from make variables

tools: generate pkg-config files from make variables

For each library built two variants of pkg-config files are created
from a per-library template: an "official" one for installation on
the user's system, and one used for building internal tools, like e.g.
qemu.

Instead of the template which is looking very similar for all libraries
generate the pkg-config files directly from make variables.

This will reduce the need to specify some pkg-config file entries in
the templates, as the contents can easily be generated from available
data (e.g. "Version:" and "Requires.private:" entries).

Especially the variant used for building internal tools needs to gain
additional runtime link parameters for the internally used libraries,
as otherwise those won't be found by the users (e.g. qemu).

Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Wei Liu <wl@xen.org>