dnsmasq: fix parallel make failure

The dnsmasq target depends on .configured and $(objs). .configured does an rm
-f *.o. Yet the only thing telling make to build the .configured target
before the $(objs) target was the order of the dependencies of the dnsmasq
target. We can't rely on that order when doing a paralllel make build, so add
an explicit rule to enforce that order.

JIRA: SB-2767

Signed-off-by: Christopher Larson <kergoth@gmail.com>