* modules/glob (Files): Add glob-libc.h.

* modules/glob (Files): Add glob-libc.h.
* lib/glob-libc.h: Renamed from glob_.h.  The new version is
taken from libc's glob.h, except with '#ifdef __GLOB_GNULIB'
protecting things that should be done only in gnulib contexts.
* lib/glob_.h: New file, containing only the glob things needed for
gnulib.
(GLOB_PREFIX): Remove.  All uses changed to look for __GLOB_GNULIB.
(__GLOB_CONCAT, __GLOB_XCONCAT, __GLOB_ID): Remove; no longer needed.
(glob, globfree, glob_pattern_p): Now defined simply in terms of
rpl_glob, rpl_globfree, rpl_glob_pattern_p.
(__GLOB_GNULIB): New macro, to keep the glob.h changes clearer
and to respect the namespace rules better.
* m4/glob.m4 (gl_GLOB_SUBSTITUTE): AC_LIBSOURCES for glob.c,
glob_.h, glob-libc.h.
(gl_PREREQ_GLOB): Remove _SYS_CDEFS_H hack; no longer needed.