Bug 26265: Add pos directory to the Makefile

Bug 26265: Add pos directory to the Makefile

This patch adds the /pos directory to the Makefile so that pos gets
properly mapped at make and install time.

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
(cherry picked from commit acbd6b72052381151f69a3b8aa70ab39cf4fda1c)

Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
(cherry picked from commit b1e7e904867d5170f3052c1d93c72ab66da7be09)