debian: create -doc subpackage with pdf manuals

I have verified, that the resulting debian packages build in my own OBS
namespace (see the -doc packages):
https://download.opensuse.org/repositories/home:/osmith42/Debian_9.0/all/
https://build.opensuse.org/project/show/home:osmith42

Depends: Ib7251cca9116151e473798879375cd5eb48ff3ad (osmo-ci)
Related: OS#3899
Change-Id: I5563e023dc3c8b158a79ce0c9e1478e117b0ec37

debian/control

@@ -7,7 +7,8 @@ Build-Depends: debhelper (>= 9),
                pkg-config,
                libdpkg-perl, git,
                dh-autoreconf,
-               libosmocore-dev (>= 0.8.0)
+               libosmocore-dev (>= 0.8.0),
+               osmo-gsm-manuals-dev
 Standards-Version: 3.9.6
 Vcs-Browser: http://git.osmocom.org/osmo-ggsn/
 Vcs-Git: git://git.osmocom.org/osmo-ggsn
@@ -74,3 +75,12 @@ Description: Debug symbols for OsmoGGSN
  .
  The library libgtp implements the GTP protocol between SGSN and GGSN
  and this package contains the development files for this library.
+
+Package: osmo-ggsn-doc
+Architecture: all
+Section: doc
+Priority: optional
+Depends: ${misc:Depends}
+Description: ${misc:Package} PDF documentation
+ Various manuals: user manual, VTY reference manual and/or
+ protocol/interface manuals.

debian/osmo-ggsn-doc.install

@@ -0,0 +1 @@
+usr/share/doc/osmo-ggsn-doc/*.pdf

debian/rules

@@ -19,4 +19,8 @@ override_dh_strip:
 	dh_strip -plibgtp4 --dbg-package=libgtp-dbg
 
 override_dh_auto_configure:
-	dh_auto_configure -- --with-systemdsystemunitdir=/lib/systemd/system
+	dh_auto_configure -- --with-systemdsystemunitdir=/lib/systemd/system --enable-manuals
+
+# Don't create .pdf.gz files (barely saves space and they can't be opened directly by most pdf readers)
+override_dh_compress:
+	dh_compress -X.pdf

doc/manuals/Makefile.am

@@ -12,5 +12,6 @@ if BUILD_MANUALS
   VTY_REFERENCE = osmoggsn-vty-reference.xml
   include $(OSMO_GSM_MANUALS_DIR)/build/Makefile.vty-reference.inc
 
+  OSMO_REPOSITORY=osmo-ggsn
   include $(OSMO_GSM_MANUALS_DIR)/build/Makefile.common.inc
 endif