uninative-tarball: Add libgcc

We ship libpthread with uninative. when uninative is active we're seeing
failures like:

   libgcc_s.so.1 must be installed for pthread_cancel to work
   Aborted

which is since we don't have a libgcc that matches libpthread. Add libgcc
to avoid these errors.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>