The open source source code for the uClibc and for the linux kernel with headers are also available in the Amazon source code release for the Kindle1. They just don't have any Amazon code.
https://www.amazon.com/gp/help/custo...deId=200203720
I imagine you would also need all of the libraries from the K1 when you link with your own programs. I haven't built much for a long time and never tried buildroot and avoid emulators so can't help there. I am about to have other things to do also. Have fun anyway.