sys-kernel/linux-headers wants 3.4, but qemu-1.1.1-r1 wants 3.1 and both are stable packages, isn't it ?
every app-emulation/qemu ebuild in the tree depends on >=sys-kernel/linux-headers-2.6.35, so obviously that isn't your problem.
I'm really confused by this bug. I really think you're using an overlay from somewhere and not realizing it due to this and the other bug you've got opened.
After I added ~sys-boot/syslinux-4.06 to /etc/portage/package.accept_keywords/misc, I've no problems and linux-headers-3.4 is installed. sys-boot/syslinux-4.064.05 however brought the trouble as soon as I run emerge --update @world --newuse --changed-use --with-bdeps=y --ask instead of my usual emerge --update @world --ask