OS X ffi in config.h

While browsing the configure generated llvm/Config/config.h, I'm noticed that
the macros:

HAVE_FFI_CALL
HAVE_FFI_FFI_H
HAVE_FFI_H

are not defined on OS X (currently 10.6.5).

Given that ffi exists on this platform (both headers and lib), is this result intended?

Thanks

Garrison

Ah, --enable-libffi.

Any pointers as why this is not a default check for at least
UNIX systems? Does Windows have the equivalent?

Thanks in advance

Garrison

IIRC it's to stop programs linked to LLVM from accidentally depending on libffi.
If your program links to it without you noticing, a binary
distribution might not run unless the user also has libffi installed.
(This used to happen even for programs that don't use the JIT, but I'm
not sure if that would still be the case)