Debugging an undefined 'make' macro (Max?)

[walt]

Heh!  Max is the 'make' guru of the known universe, but I would
welcome an answer from anyone else who knows the answer :o)
Background:  I'm trying to build the pkgsrc/wip/jdk14 package
on DFly, and I'm hitting the limits of my knowledge about how
'make' works.
I'm able to figure out that the build fails on DFly because the
variable ${PLATFORM} is undefined.  The question is:  where does
it become defined on NetBSD and, more important, how to debug the
problem in general on other systems?
To be specific:  I know that 'make -V [variable]' should give
me the value of the variable as it is understood by 'make'.  But
when I do 'bmake -V PLATFORM' on DFly (and NetBSD also) I get no
answer (i.e. the nullstring).
At some point in the build process the PLATFORM variable becomes
defined -- or else the build would fail on NetBSD as well as DFLY.
So -- how, in general, can I debug this kind of problem?

If you can tell by reading this question that I am missing some
basic newbie skills, *please* refer me to the basic documents I
need to study!
Thanks!