disruptive libffi upgrade

[Colin Walters]

On Fri, 2012-04-13 at 20:58 -0400, Anthony Green wrote:
> Sorry folks -- thanks for untagging.  I'll ping the list again after May 9, as was suggested earlier in this thread.

Here's a lightly tested patch which implements my suggestion of keeping
the symbols as empty stubs.

Incidentally - keeping the generated autotools stuff in git makes
tracking down what *really* changed extremely painful.  It looks
like the ABI was bumped in ee6696fdf4768ba6dd037fb6dd99435afa13816e
but that commit has thousands of lines of generated code changes
too.  It'd be better to either:

1) Do "regenerate autotools" as a separate commit
2) Keep a separate git repository with generated stuff
3) Don't commit the generated files, have consumers install
   the autotools, and join the rest of the world