Replace some -ldl by $(DLOPEN_LIBS)
Add some FREEBSD tests

Change-Id: Ic30fe29b938d877694db2927775f89de15c02d87
Reviewed-on: https://gerrit.libreoffice.org/20652Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Matúš Kukan <matus@libreoffice.org>