The copy of libffi for PLT Scheme has been changed in a few small
ways:

 * Added i386 Mac OS X support from the PyObjC project:
     gcc/libffi/src/x86/ffi_darwin.c
     gcc/libffi/src/x86/darwin.S
   and changed ffi.c and sysv.S to #include these when __APPLE__
   is defined.

 * Added line to "configure" for i*86-*-darwin*

 * Added line to "configure" for i*86-*-openbsd*
