getopt-posix: detect MacOS bug

getopt-posix: detect MacOS bug

On MacOS 10.5 (Darwin 9.8.0), optind is incremented by 2 instead
of 1 in the case of a missing requirement on condensed options.

* m4/getopt.m4 (gl_GETOPT_CHECK_HEADERS): Reject MacOS botch of
optind when missing a required argument.
* doc/posix-functions/getopt.texi (getopt): Document the bug.
* doc/glibc-functions/getopt_long.texi (getopt_long): Likewise.
* doc/glibc-functions/getopt_long_only.texi (getopt_long_only):
Likewise.

Signed-off-by: Eric Blake <eblake@redhat.com>