As described in the README, I do $ ./bootstrap$ ./configure --with-platform=grub-emu --build=x86_64 --target=x86_64 --host=x86_64 (plus setting some directories because I am on NixOS)
Well, should have been --with-platform=emu, not grub-emu. It builds fine with '--with-platform=emu --target=x86_64 --enable-grub-emu-sdl --disable-grub-emu-pci'
Alex
