I'd suggest downgrading to version 4.3.5, and applying the set of patches that Debian currently uses. The patches are here (debian/bsdpatches directory):
http://ftp.de.debian.org/debian/pool/main/g/gcc-avr/gcc-avr_4.3.5-1.tar.gz
(this is just the patches, you'll need to download the GCC 4.3.5 source as well from gcc.gnu.org)
Binutils may also need Debian patches.
http://ftp.de.debian.org/debian/pool/main/b/binutils-avr/binutils-avr_2.20.1-1.tar.gz