I don't even know how to build OpenBIOS, so I'm not going to fix it, sorry.
If you have a PPC cross-compiler installed,
$ du -sh ~/cross/ 4.5G /home/segher/cross/
Yeah, I have a PowerPC cross-compiler.
the build is easy:
./config/scripts/switch-arch cross-ppc make
Then copy the resulting binary from obj-ppc/ into your share/qemu directory.
...but qemu hasn't worked for me for many years. Maybe I should try again, sigh.
Find me on IRC?
Segher