* lib/getloadavg.c: Use __VMS, not VMS.

* lib/getloadavg.c: Use __VMS, not VMS.
* lib/getopt.c: Likewise.
* lib/getpagesize.h: Likewise.
* lib/glob.c: Remove most VMS cruft; it hasn't been tested for a while and
probably does not work.
* lib/backupfile.c [HAVE_DIRENT_H && ! HAVE_NDIR_H]:
Don't worry about this obsolete case any more.
(HAVE_DIR): Remove.  All uses removed; we now assume you can read
directories.
* lib/dirfd.h [HAVE_DIRENT_H && ! HAVE_NDIR_H]: Don't
worry about this obsolete case any more.
* lib/fts.c: Likewise.
* lib/getcwd.c: Likewise.
* lib/glob.h: Likewise.
* lib/savedir.c: Likewise.
* m4/backupfile.m4 (gl_BACKUPFILE): Check for dirent.h, instead
of invoking obsolescent AC_HEADER_DIRENT macro.
* m4/d-ino.m4 (gl_CHECK_TYPE_STRUCT_DIRENT_D_INO): Likewise.
* m4/d-type.m4 (gl_CHECK_TYPE_STRUCT_DIRENT_D_TYPE): Likewise.
* m4/dirfd.m4 (gl_FUNC_DIRFD): Likewise.
* m4/fts.m4 (gl_FUNC_FTS_CORE): Likewise.
* m4/getcwd.m4 (gl_PREREQ_GETCWD): Likewise.
* m4/glob.m4 (gl_PREREQ_GLOB): Likewise.
* m4/savedir.m4 (gl_SAVEDIR): Likewise.
* m4/readdir.m4: Remove; no longer needed.