build: parallel build: require ../libosmo-ranap.la from tests/

This rule is bad because it re-invokes $(MAKE), but it seems to fix the
parallel build. It should probably be done differently.

Change-Id: I8107e08e4c211f20d671f520bf6bab9356f3c90e
diff --git a/src/tests/Makefile.am b/src/tests/Makefile.am
index 3a99681..5b51262 100644
--- a/src/tests/Makefile.am
+++ b/src/tests/Makefile.am
@@ -27,6 +27,9 @@
 dummy_cn_SOURCES = $(RANAP_FILES) test_common.c dummy_cn_sua.c
 dummy_cn_LDADD = $(COMMON_LIBS) $(top_builddir)/src/libosmo-ranap.la
 
+$(top_builddir)/src/libosmo-ranap.la:
+	$(MAKE) -C $(top_builddir)/src libosmo-ranap.la
+
 # The `:;' works around a Bash 3.2 bug when the output is not writeable.
 $(srcdir)/package.m4: $(top_srcdir)/configure.ac
 	:;{ \