GCC 4.2 made it to testing. I don't expect compatibility problems for
gcc itself, but I do expect gcj and fortran programs to break: libgcj
and libfortran bumped soname. This means all fortran apps that link
against libfortran will need a rebuild and that all apps that have been
compiled to native code with gcc-gcj will need a recompile. These
programs will get recompiled soon.
For gcc-gcj, I don't expect any program to use native code, the only one
I've seen for now is gjdoc, which is already built with it.
The new GNU hashing style supported by gcc 4.2.0 isn't included, our
binutils and glibc don't support it. I've read something about 2MB
bigger libraries because of another extra hashtable added to every lib,
so I don't feel much for backporting or switching to a 2.17.xx binutils