This fixes handling of collating symbols in fnmatch (glibc bug 26620).
This does not affect Gnulib; it merely keeps Gnulib and glibc
closer together, to help with any eventual merge, by incorporating
a recent glibc patch. The patch and the following commentary is
by Andreas Schwab.
* lib/fnmatch_loop.c (FCT) [WIDE_CHAR_VERSION]: The variable idx
contains the index into the extra array, whereas wextra points
into the extra array at this index, containing the length of the
following collating sequence in the wide character representation.