How to make INSTALLS_DEPENDS?

[walt]

I'm not the only one who is seeing this error message recently when
trying to build a port which has dependencies:

Don't know how to make INSTALLS_DEPENDS

This variable appears in /usr/ports/Mk/bsd.port.mk and is obviously
not intended to be a make target at all, but 'make' is interpreting it
that way for some reason.

Can anyone explain this recent problem?  Seems it has appeared just in
the last two or three days.