Built gcc on amd64 with and without lib32, and with and without the new
MULTILIB option. I could not really observe differences. Did the same in
powerpc64, and "gcc -print-multi-lib" indeed showed different results. More
importantly, gcc now builds fine on powerpc64 out of the box.
Now testing gcc48 and gcc49. (The builds take a long time, so I'd rather
parallelize the review process with the actual build testing...)
I don't want to bother testing older gcc versions, hence why they are not
included in this patch.