Fixing ULIMIT_CMD_virtualsize fallout

[Jonathan Perkin <jperkin%joyent.com@localhost>]

Joerg's addition of ULIMIT_CMD_virtualsize broke non-NetBSD platforms
when packages use limits, for example lang/rust.

One option is to add ULIMIT_CMD_virtualsize?=: to all platform/*
files, another is this diff I wrote:

  --- bsd.pkg.mk	9 Feb 2020 22:39:20 -0000	1.2035
  +++ bsd.pkg.mk	26 Mar 2020 11:04:18 -0000
  @@ -231,7 +231,7 @@
   _NONZERO_FILESIZE_P=	${AWK} 'END { exit (NR > 0) ? 0 : 1; }'
   
   # Automatically increase process limit where necessary for building.
  -_ULIMIT_CMD=		${UNLIMIT_RESOURCES:@_lim_@${ULIMIT_CMD_${_lim_}};@}
  +_ULIMIT_CMD=		${UNLIMIT_RESOURCES:@_lim_@${ULIMIT_CMD_${_lim_}:U\:};@}
   
   _NULL_COOKIE=		${WRKDIR}/.null
   

Opinions on preferred fix?

-- 
Jonathan Perkin  -  Joyent, Inc.  -  www.joyent.com