Excellent, we're getting somewhere. I've pushed another patch to correct that.
Unfortunately I'm completly guessing as to which files need to be compiled for libffi to work on ppc platforms.
If it doesn't work you could try fiddling with the files listed in /local/d0p6/aw/yhc/build, line 25. The files in that list need to be taken from yhc/depends/ctypes/libffi/src/powerpc (apart from the first two).
Andrew