Subject: Re: Help with building a kernel
To: None <port-vax@NetBSD.ORG, tst@titan.cs.mci.com>
From: Charles M. Hannum <mycroft@domino.org>
List: port-vax
Date: 02/07/1996 03:59:46 
   [...]
   "/usr/share/mk/bsd.own.mk", line 62: Malformed conditional ((${MACHINE_ARCH} ==
 "alpha"))
   [...]

It sounds like your make(1) is too old to understand MACHINE_ARCH.
Either upgrade it, or use:

make 'MACHINE_ARCH=vax'

and it should work okay.