Use release helper from libosmocore

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

Change-Id: I869395d5c9ab5ec1a487aff15418d1517f47e831
Related: OS#1861
diff --git a/configure.ac b/configure.ac
index 871f7e5..b0d6b23 100644
--- a/configure.ac
+++ b/configure.ac
@@ -12,6 +12,10 @@
 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