Cannot build -current with port-sparc64?

For reasons that are unknown to me, any attempt to build -current
on 6.99.28 fails when it tries to compile the first .c file that
isn't part of tools.

The error messages can be found here:
http://mail-index.netbsd.org/current-users/2014/05/20/msg024921.html

It was pointed out to me that TOOLDIR cannot be inside of DESTDIR,
so I reran the build with

./build.sh -u -j4 -T /tooldir build

and DESTDIR in Makefile.local.inc still pointing to /current and
it still fails in exactly the same way.

What's wrong?

Darren