Ensure the linker supports @unwind sections in libffi. From Mozilla bug 756740.
https://bugzilla.mozilla.org/show_bug.cgi?id=778414

Also tracked as issue #42.
https://github.com/atgreen/libffi/issues/42
Remove stray hunk that shouldn't have been included in this patch.
Ensure the linker supports @unwind sections in libffi.