HEADS UP: TOOLBASE/LOCALBASE split

[Taylor R Campbell <riastradh%NetBSD.org@localhost>]

FYI: I just committed the changes I proposed earlier this month to
split TOOLBASE out of LOCALBASE for the sake of cross-compilation:

- TOOLBASE: prefix where toolchain programs in packages installed as
  TOOL_DEPENDS can be executed from

- LOCALBASE: prefix where run-time dependencies of the package being
  built will generally be installed (possibly distinct from PREFIX,
  which is where the package being built will be installed)

This way, you can cross-compile packages that install to /usr/pkg, but
run the build unprivileged with toolchain programs under ~/cross/pkg.

I also committed a host of changes to respect this split in various
packages.  I tried to keep the changes reasonably minimal, and mostly
restricted to the case where USE_CROSS_COMPILE is enabled, so there
shouldn't be too much fallout.

But it's possible I made mistakes, so I'll be monitoring the bulk
build reports closely -- and if I miss anything, please don't hesitate
to contact me about anything I broke!