It used by node-waf script, that used for build binary C++ addons.
As I understand he, Ryan is trying to avoid external dependencies and
make Node.js installation easier therefore includes all the necessary
tools and libraries in the distribution.
If I understand correctly, this is not about porting Node.js to the
OpenBSD platform, where it is already runs on, but about establishment
of port for installation (I'm from Linux land and don't know *BSD so
deep). I think in this case, you can exclude wafadmin from the port
(as well as V8 and c-ares, maybe), leaving only node_addon.py