ppc: switch handling of 'foreign import wrapper' (FIW) to libffi
Joseph Jezak reported darcs-2.4.4 SIGSEGV in interactive mode in ghc-6.12.3.
So I've concluded ppc also has rotten native adjustor. I don't have hardware
to verify the patch (ticket Trac #3516 should help to test it), but I think it will
help (as similar patch helped for ia64 and ppc64).