After some discussion in #grub, I was told that the --enable-efiemu and --enable-grub-pe2elf options should not be set. The former is for booting Darwin and depends on the "Large memory model support" compiler feature (at least, that's what that random guy in IRC told me), and the latter is used to convert the grub binary from PE to ELF, which is only needed when it is built on windows (and afaik, gentoo doesn't run on windows /yet/. this would be a very interesting GSoC project ;-)). Reproducible: Always Steps to Reproduce: ps: for me, it solved a build error in a funtoo chroot.
http://sources.gentoo.org/sys-boot/grub/grub-9999.ebuild?r1=1.10&r2=1.11