freebsd: dlopen/dlsym/dlerror is part of libc, use LIBRARY_DL for linking
In FreeBSD there is no spearate library for dlopen, dlsym and dlerror.
Use LIBRARY_DL to check for this condition.
diff --git a/openbsc/src/osmo-nitb/Makefile.am b/openbsc/src/osmo-nitb/Makefile.am
index ce2f25d..53a1b40 100644
--- a/openbsc/src/osmo-nitb/Makefile.am
+++ b/openbsc/src/osmo-nitb/Makefile.am
@@ -15,6 +15,6 @@
$(top_builddir)/src/libtrau/libtrau.a \
$(top_builddir)/src/libctrl/libctrl.a \
$(top_builddir)/src/libcommon/libcommon.a \
- -ldbi -ldl $(LIBCRYPT) \
+ -ldbi $(LIBRARY_DL) $(LIBCRYPT) \
$(LIBOSMOGSM_LIBS) $(LIBOSMOVTY_LIBS) $(LIBOSMOCORE_LIBS) \
$(LIBOSMOABIS_LIBS) $(LIBSMPP34_LIBS)