build: update gnulib submodule to latest

build: update gnulib submodule to latest

Coreutils mistakenly did not list xstrndup as a module
that it depends on directly.  When the latest Gnulib removed
the dirname module's dependency on xstrndup, this mistake
caused coreutils to not build.  Since all of Coreutils's
uses of xstrndup know the string length, xmemdup0 is a better
match for what's needed.  Since the size args are typically
signed or derived from subtracting pointers, the new Gnulib
ximemdup0 function is a better match yet.
So, use ximemdup0 instead of xstrndup.
* src/cut.c, src/dircolors.c, src/expand-common.c, src/expand.c:
* src/numfmt.c, src/set-fields.c, src/unexpand.c:
Do not include xstrndup.h; no longer needed.
* src/dircolors.c (parse_line):
* src/expand-common.c (parse_tab_stops):
* src/numfmt.c (parse_format_string):
* src/set-fields.c (set_fields):
Use ximemdup0 instead of xstrndup.