Report 3 — Multiarch cross-toolchains

Hi,
Here is my fourth report on the “Multiarch cross-toolchains” project[0],
mentored by Héctor Orón and co-mentored by Marcin Juszkiewicz.

First, I have to admit I've been slacking a bit since the midterm evaluation.
I'm a bit late according to my original planning, as I should be in the middle
of figuring out what changes to wanna-build, buildd, sbuild, britney and such
are needed to support cross-arch deps in the archive, as well as working on a
way to automate building cross-compilers so it can get in the archive.

However, there has been a slight change in the planning: indeed, during
Debconf, the issue of libstdc++6-4.7-dev depending on g++-4.7 (#678623) was
discussed[1], and the proposed solution was to split gcc-4.7 in two packages,
and likewise for the other compilers such as gfortran or gobjc.
I've started to work on this, and I have a first patch waiting for reviews.
However, such a change would introduce file conflicts between the “old”
gcc-4.7/gcc-4.7-multilib packages and the new lib*gcc1-*-dev ones, meaning that
those packages must conflict with older versions of gcc-4.7/gcc-4.7-multilib.
Unlike my previous patches, it's useless and actually harmful to provide
third-party packages implementing this change until it gets in Debian.

I've also built amd64 (target) single-lib and multilib cross-compilers for i386.
While it may seem useless (gcc-multilib for i386 just does the same), it enabled
me to spot and fix a few errors I've made in an earlier patch, as well as a few
other issues that may affect many other arches too.
This means that things like sparc→i386 or sparc→amd64 cross-compilers (which
are things I've seen requests for a couple of time) should now build and work
properly, although I have no sparc hardware to confirm!
I plan on trying other arches (mips, mipsel, powerpc, sparc...) in the following days.