gmake by setting GMAKE_J_ARGS=-jN.
discussed with matt@ and a few others.
XXX: this is kind of hacky, as it will fork off more processes than
XXX: "-jN" says to, but there's no real way to get parallelism in
XXX: both the tools/gcc build and the rest of the build without
XXX: this.
work on all currently supported netbsd build hosts.
XXX current issues:
XXX - calls /usr/bin/env -i directly, mostly to wipe-out MAKEFLAGS
XXX from the environment (usually set by the buildwrapper to
XXX "-de -m <path-to>/share/mk"
