We have been using OpenIndiana Illumos for our Advanced OS course. I faced a bit of difficulty installing essentials on it, hence this blog post to keep track of what I did to fix it.
$ sudo pkg uninstall entire
$ sudo pkg update -v
$ pkg set-publisher -O http://pkg.openindiana.org/hipster-2015 --search-first openindiana.org
$ sudo pkg install build-essential
Helped me, hope it helps someone!