- added gcc_libffi bcond; now it's possible to use separate libffi for system-wide use:
  libgcj and libgo always have gcc libffi as convenience library linked in
  libgtkpeer (and its libjawt version) uses system libffi if gcc libffi is not installed on build
  note: upstream default as of gcc 4.8.x is not to package gcc libffi as system-wide