bsd.README says:

 It's fairly difficult to make the BSD .mk files work when you're building
 multiple programs in a single directory.  It's a lot easier to split up the
 programs than to deal with the problem.  Most of the agony comes from
 making the "obj" directory stuff work right, not because we switched to a
 new version of make.  So, don't get mad at us, figure out a better way to
 handle multiple architectures so we can quit using the symbolic link stuff.
 (Imake doesn't count.)

Can somebody please tell me exactly what the problem is?

My goal is to find a way to provide equivalent functionality to automake
using a pmake derivative (*BSD make, basically) and a set of .mk files.

(Please Cc: me on any replies; I'm not on the list.)

H