Hi,

on Ubuntu 10.04 x86_64 LTS. I of course had to install gcc-4.7 first, but that was easy to find on the Internet.

We no longer support iMX53 and iMX6 (that's why there's no JB build) - so nobody has tried to build this in a while.
That said, we didn't do anything that should break it (and if you do any work on it, we'd be glad to have it in our repositories as a community build).
Did you get gcc 4.7 from the right place? (You need a version w/ Android support, a typical gcc build won't do).
The toolchain you want is probably https://android-build.linaro.org/builds/~linaro-android/toolchain-4.7-bzr/
 
My problem it seems is some lines like the following (for libgcc_s.so and libgcc.a too):

/usr/bin/ld: skipping incompatible /usr/lib/gcc/x86_64-linux-gnu/4.7/libstdc++.so when searching for -lstdc++

You need to install a 32bit environment on your machine.
The Android toolchain is 32bit (even though other parts of the build system need a 64bit machine - I think it's stupid, but it's the way AOSP decided to do it), so the host tools will be built in 32bit mode - meaning you need a 32bit libstdc++ and libc to link to.

ttyl
bero