[Yhc] What does Yhc need (error, ffi.h not found)

[Isaac]

Trying scons on a freshly darcs'd yhc from today, I got an error, see:
http://paste.lisp.org/display/22129
or, to include the relevant parts of the output here:

gcc -I. -c -o src/runtime/BCKernel/external.o
src/runtime/BCKernel/external.c
In file included from src/runtime/BCKernel/types.h:5,
                 from src/runtime/BCKernel/hashtable.h:4,
                 from src/runtime/BCKernel/module.h:18,
                 from src/runtime/BCKernel/external.h:4,
                 from src/runtime/BCKernel/external.c:1:
src/runtime/BCKernel/platform.h:103:17: ffi.h: No such file or directory
scons: *** [src/runtime/BCKernel/external.o] Error 1
scons: building terminated because of errors.

On IRC, ndm suggested that "libffi" was needed; after "emerge libffi"
the error still happened -- so, me being on gentoo-linux ppc, ndm on
Windows, referred me to this list. I'm trying to find out what is
actually needed to successfully compile Yhc (now, for me, at least).