Fix build error on Solaris 11 in 32-bit mode.
Reported by Kiyoshi KANAZAWA <yoi_no_myoujou@yahoo.co.jp> in
<https://lists.gnu.org/archive/html/bug-gettext/2020-07/msg00034.html>.
* gnulib-local/lib/getopt-core.h.diff: Don't include <config.h> if it has
already been included. This fixes the compilation of vma-iter.c.
