Nitdroid is essentially "android built for N9".
Yes, it seems that Alexey has worked on it for awhile, but it was not ready.

The general procedure for building Android for any device is same. The main difference is the manifest you use. You can get started with the last section of this post: https://thp.io/2012/nitdroid/
(Build Android AOSP (Nitdroid flavor) from source). A similar post was available in Nitdroid forum, which seems to be down...

You'd probably better to start from the last commits by Alexey. However, you cannot simply build android for an unsupported device and expect it to work.