The version of busybox shipped with genkernel is currently not compatible with GCC4, however this is easily fixed: sys-apps/busybox-1.00-r4 (marked as stable) uses a patch (attaching) which fixes the compilation-problem. Genkernel-3.2.9 gives with and without the patch (before 'Compiling BusyBox') some funny output during the creaton of initrd. Should look into that too now to see if it has something to do with GCC4 too, but I guess thats another bug-report.
Created attachment 63865 [details, diff] Patch for busybox as in portage The patch applies cleanly on my system and genkernel works after.
Fixed in 3.3; thanks!