gnulib: upgrade to today's version
* tools/snippet/_Noreturn.h, tools/snippet/c++defs.h,
tools/snippet/arg-nonnull.h, tools/snippet/warn-on-use.h: Rename to...
* lib/_Noreturn.h, lib/c++defs.h, lib/arg-nonnull.h,
lib/warn-on-use.h: ... these.
* lib/filename.h, lib/getopt-cdefs.in.h, lib/getopt-core.h,
lib/getopt-ext.h, lib/getopt-pfx-core.h, lib/getopt-pfx-ext.h,
lib/localtime-buffer.c, lib/localtime-buffer.h, lib/malloca.c,
lib/malloca.h, lib/malloca.valgrind, lib/stat-w32.c, lib/stat-w32.h,
m4/eealloc.m4, m4/localtime-buffer.m4, m4/malloca.m4: New files.
* lib/argp-help.c, lib/argp-parse.c, lib/error.c, lib/float.in.h,
lib/getopt1.c, lib/getopt.c, lib/getopt.in.h, lib/getopt_int.h,
lib/gettext.h, lib/gettimeofday.c, lib/intprops.h, lib/isatty.c,
lib/limits.in.h, lib/localcharset.c, lib/Makefile.am, lib/mbrtowc.c,
lib/mbsinit.c, lib/msvc-nothrow.c, lib/quotearg.c, lib/stat.c,
lib/stdalign.in.h, lib/stdint.in.h, lib/string.in.h,
lib/sys_stat.in.h, lib/sys_types.in.h, lib/tempname.c, lib/time.in.h,
lib/unistd.in.h, lib/vasnprintf.c, lib/wchar.in.h, lib/wctype.in.h,
lib/xalloc.h, lib/xalloc-oversized.h, m4/fcntl-o.m4, m4/float_h.m4,
m4/getopt.m4, m4/gettimeofday.m4, m4/gnulib-common.m4,
m4/gnulib-comp.m4, m4/include_next.m4, m4/largefile.m4, m4/lstat.m4,
m4/mbrtowc.m4, m4/memchr.m4, m4/mkstemp.m4, m4/printf.m4, m4/sleep.m4,
m4/stat.m4, m4/stdalign.m4, m4/stdint.m4, m4/strerror.m4,
m4/string_h.m4, m4/sys_stat_h.m4, m4/sys_time_h.m4, m4/sys_types_h.m4,
m4/time_h.m4, m4/unistd_h.m4, m4/wchar_h.m4, m4/wctype_h.m4,
m4/wint_t.m4: Update.
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