auto* versions for gcc?

[Bonzini]

> Paolo (on copy) has libffi configury fixes to bring it up to modern
> standards.  I don't know the status of these changes.  Unfortunately,
> the discussion for these changes is happening on a non-GNU list to which
> I'm not subscribed and I can't seem to find the archives for.

BTW, there is another problem.  libffi includes ffi_config.h.in in public headers which
is a bad bad thing.  I can make a patch for this, can you (Anthony) review it?

Paolo