Off topic, but this information may be useful for the Alopex guys as they're targeting thumb only at the moment because of reliance of its' gcc version.

With regards to circular dependencies, this is the same sort of issue I was facing when trying to build Debian from scratch a few years back, dropping i386 support in favour of a pure i686 build instead of only certain packages. I just had some time to kill whilst playing about IIRC I had built a toolchain using a mix of LFS and Debian patches with its own version feature stripped version of apt and dpkg. This way I could use dpkg-buildpackage to build the debs of the system but install them using a different root. I think I hit an issue when rebuilding apt or dpkg because of a dependency on po4a (again...IIRC) but it needed dpkg to be built with certain features enabled, which couldn't be done without po4a built.

Glad they now make this clearer on the wiki.