Reported by Daurnimator <quae@daurnimator.com> in
<https://lists.gnu.org/archive/html/bug-libunistring/2016-11/msg00010.html>.
* lib/gen-uni-tables.c (struct mirror_pair): New type.
(mirror_pairs): Don't initialize statically.
(mirror_pairs_count): New variable.
(fill_mirror): New function.
(get_mirror_value): Update.
(main): Expect the file name of BidiMirroring.txt as command-line
argument. Invoke fill_mirror.
* lib/unictype/mirror.h: Regenerated.