I've sent in a pr for that.   Here's a patch that should solve the
problem:

Index: Makefile
===================================================================
RCS file: /a/cvsroot/src/usr.bin/vmstat/Makefile,v
retrieving revision 1.13
diff -c -r1.13 Makefile
*** Makefile	1994/12/28 18:39:53	1.13
--- Makefile	1995/05/04 23:15:16
***************
*** 2,8 ****
  #	$Id: Makefile,v 1.13 1994/12/28 18:39:53 mycroft Exp $
  
  PROG=	vmstat
! .if (${MACHINE_ARCH} == "m68k")
  CFLAGS+=-D${MACHINE} -I${.CURDIR}/../../sys/arch
  .endif
  MAN=	vmstat.8
--- 2,8 ----
  #	$Id: Makefile,v 1.13 1994/12/28 18:39:53 mycroft Exp $
  
  PROG=	vmstat
! .if (${MACHINE_ARCH} == "m68k" || ${MACHINE_ARCH} == "mips")
  CFLAGS+=-D${MACHINE} -I${.CURDIR}/../../sys/arch
  .endif
  MAN=	vmstat.8