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

Makefile.am

@@ -21,6 +21,9 @@ pkgconfig_DATA = openbsc.pc
 
 BUILT_SOURCES = $(top_srcdir)/.version
 EXTRA_DIST = git-version-gen osmoappdesc.py .version
+
+@RELMAKE@
+
 $(top_srcdir)/.version:
 	echo $(VERSION) > $@-t && mv $@-t $@
 dist-hook:

configure.ac

@@ -12,6 +12,10 @@ AC_CONFIG_TESTDIR(tests)
 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