when -march=native is enabled for gcc 4.3, an emerge gcc-3.3.6 will fail due to missing filter rules. Apparently, the CFLAGS are passed over to the gcc-3.3.6 build without removing/replacing this particular switch.
This bug prevents sun-jdk from being built.
use sys-libs/libstdc++-v3 instead of gcc-3.3
any flag that a gcc version doesn't support will cause an error when building that version. we can't filter them all. temporarily change -march to something gcc-3.3.6 understands.
This helps much. As for solving the problem entirely: is there no possibility to prevent GCC from being bootstrapped (including the new CFLAGS), if the original compiler is GCC and has a higher version number (in this case 4.3.1) ? That way, we would have solved this problem once and for all!
Anyways, thank you very much for the quick help!