I've committed some changes to make's handling of command line
variable assignments via MAKEFLAGS.
1. the values are 'quoted'
2. when adding name='value' any previous name=* is removed.
3. the vars are not recorded directly in MAKEFLAGS, but in
.MAKEOVERRIDES and MAKEFLAGS is re-exported if .MAKEOVERRIDES is
assigned to.  Thus
.MAKEOVERRIDES=
can be used to disable the export of command line variable assignments
via MAKEFLAGS.  This is comparable to the way gmake does it btw.

With these changes, my testing in pkgsrc looks ok.
Though there may still be cases that may break - in which case adding
.MAKEOVERRIDES=
to bsd.pkg.mk may be necessary.

I'll update make.1 when I get a chance.
--sjg