Use release helper from libosmocore

See
https://osmocom.org/projects/cellular-infrastructure/wiki/Make_a_new_release
for details.

Change-Id: Iafe5905895a656b7055d58ca8f745fcfa4bd9886
Related: OS#1861
diff --git a/Makefile.am b/Makefile.am
index 798c092..6caa009 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -4,6 +4,9 @@
 
 BUILT_SOURCES = $(top_srcdir)/.version
 EXTRA_DIST = git-version-gen .version
+
+@RELMAKE@
+
 $(top_srcdir)/.version:
 	echo $(VERSION) > $@-t && mv $@-t $@
 dist-hook:
diff --git a/configure.ac b/configure.ac
index 4c0a12f..b370e0d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -9,6 +9,10 @@
 dnl kernel style compile messages
 m4_ifdef([AM_SILENT_RULES], [AM_SILENT_RULES([yes])])
 
+dnl include release helper
+RELMAKE='-include osmo-release.mk'
+AC_SUBST([RELMAKE])
+
 dnl checks for programs
 AC_PROG_MAKE_SET
 AC_PROG_CC