.if !target(foo) equivalent?

[mcmahill]

Is there a test to see if a target has been defined?  I'd like to do
something like what you'd find in BSD make:

.if !target(foo)
.PHONY: foo
foo:
.endif

in a .mk file which I can include to make sure a certain predefined set of
targets exist.  I only want to define them if they haven't been already
defined.  

Thanks
-Dan