Hmm. It appears that the majority of the stuff in the Maemo toolchain is for the "MADDE" (Maemo Application Development and Debugging Environment) system. I can see a suite of MADDE related tools (much of which appears to be Debian-related package management), a variety of GCC libraries, and what looks to be a collection of the libraries associated with the Maemo Fremantle OS. (Not that I am any sort of expert on what goes into these toolchains...)

There's a wiki page covering MADDE.

It appears that much of MADDE is indeed available as open source; there's a Gitorious page containing that code...

Yeah, browsing through the source code, it does look like MADDE depends on some binaries provided by Nokia. The heart of the toolchain still lies elsewhere...