GCC 4.7 is now the default for x86 architectures

GCC 4.7 is now the default for x86 architectures for all frontends except the D
frontends, including KFreeBSD and the Hurd.

There are still some build failures which need to be addressed. Out of the ~350
bugs filed, more than the half are fixed, another quarter has patches available,
and the remaining quarter isn't blocking any other 4.7 build failures. Many
thanks to the patch submitters and NMUers, including Cyril Brulebois, Gregor
Herrmann, Paul Tagliamonte for the fixes.

This will add one more transition for x86 (libobjc3 -> libobjc4), which needs
starting with uploads of some GNUstep base packages.

The D v2 frontend is likely to be updated to 4.7 before the freeze (no build
dependencies).

  Matthias