There is a crosstool environment. But I don't think that you can build from that cdrom image a complete firmware image. These are only the opensource bits and until now there are no custom images for N9.

Scratchbox as the cross-compilation and development environment

Scratchbox as the cross-compilation and development environment manual installation.

Use existing ones go best for the docker image:

Docker Image
Vbox image

Power Kernel sources and instruction.

Interesting

It could be that when you use google or our search that you will get more informations. So use my links as starting point.