Makefile.am: Fix dependency of server on libosmo-rspro.la

Change-Id: I0a1badfa44479ff771be7062a19fd842f3d56b41
diff --git a/src/server/Makefile.am b/src/server/Makefile.am
index fe937b6..5926dee 100644
--- a/src/server/Makefile.am
+++ b/src/server/Makefile.am
@@ -12,3 +12,8 @@
 remsim_server_LDADD = $(OSMOCORE_LIBS) $(OSMOGSM_LIBS) $(OSMOABIS_LIBS) \
 		      $(ULFIUS_LIBS) $(JANSSON_LIBS) \
 		      $(top_builddir)/src/libosmo-rspro.la
+
+# as suggested in http://lists.gnu.org/archive/html/automake/2009-03/msg00011.html
+FORCE:
+$(top_builddir)/src/libosmo-rspro.la: FORCE
+	(cd $(top_builddir)/src && $(MAKE) $(AM_MAKEFLAGS) libosmo-rspro.la)