* backupfile.c, dirfd.h, fts.c, getcwd.c, glob.c, glob_.h:

* backupfile.c, dirfd.h, fts.c, getcwd.c, glob.c, glob_.h:
Ignore the obsolescent !HAVE_DIRENT_H case.  Consolidate NAMLEN
macros into the GNU _D_EXACT_NAMLEN.
* savedir.c:  Likewise.
(savedirstream): Use _D_EXACT_NAMLEN in preference to strlen.

* backupfile.m4, d-ino.m4, d-type.m4, dirfd.m4, fts.m4, getcwd.m4:
* savedir.m4:
Ignore the obsolescent !HAVE_DIRENT_H case.  Consolidate NAMLEN
macros into the GNU _D_EXACT_NAMLEN.