pkgsrc relies on make's ":u" modifier, which is not present in old
versions of make.

We already have PKGSRC_REQUIRED, which is supposed to check that
the pkg_install, pkg_add and freinds are sufficiently recent.  I think
that something similar should also be used to check that make is
sufficiently recent.

For example, on a NetBSD-1.5.2 box, I updated to current pkgsrc, and the
PKGTOOLS_REQUIRED test correctly forced me to update pkg_install, but I
keep getting errors saying "make: Unknown modifier 'u'".

I don't know the correct way to fix this problem.

--apb (Alan Barrett)