(Der Rest des Eintrags ist in Englisch, um möglichst viele Leser zu erreichen.)

Don't even think about checking what kernel or linux-headers you've got installed. Most likely you're trying to install a new Gentoo system, but have not booted from a recent Gentoo LiveCD, but rather some other LiveCD or chroot'ed into your installation. A quick uname -a will reveal that you're indeed not using a kernel >=2.6.9, because the LiveCD (or host system) you're using for your installation uses an older one. It's the running kernel that matters, not the one you've installed in your new Gentoo system.

Workaround: Use a newer LiveCD. If that's not possible, add "-nptl" to your USE-Flags, compile glibc, finish the installation, reboot into your new Gentoo system, remove "-nptl" again, recompile the glibc.