Unix build: have the makedepend and cc actions in one recipe

In the case of using an independent makedepend, we had split that into
two separate recipes, one depending on the other.  However, there are
cases where the makedepend recipe was always trying, but doesn't
update the time stamp of the .d file because there are no actual
changes, and thereby causing constant updates of the object files.

This change makes one recipe that takes care of both makedepend och
cc, thereby avoiding these extra updates.

Reviewed-by: Andy Polyakov <appro@openssl.org>