OS X ffi in config.h

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


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?



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


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)