From Gentoo Wiki
The problem: how to install and maintain Gentoo on low powered hardware.
The solution: build and packages in a chroot on a faster machine.
This is a system I have been using for a number of years, since I first started using an Atom-powered netbook, although I have used it with other hardware since then. However, I have only used Intel hardware, both for the build platform and the targets. I have not tried mixing Intel and AMD, so any feedback on the viability of this would be welcome.