The libffi in the F15 buildroot is completely FUBAR: it doesn't
work with hardfp at all.
There's new RPMs at
http://aph.fedorapeople.org/rpmbuild/RPMS/armv7hl/libffi-*3.0.10rc9-1.fc1...
This is cut from the development sources, so isn't a real libffi release,
but is a lot better than the one you have at the moment.
Andrew.