In BUGS section, append a warning to not use '-' as the first character

of optstring to avoid a semantic conflict with GNU getopt.

src/lib/libc/stdlib/getopt.3

@@ -29,9 +29,9 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.\"	$OpenBSD: getopt.3,v 1.19 2002/12/04 21:42:22 millert Exp $
+.\"	$OpenBSD: getopt.3,v 1.20 2002/12/08 18:12:50 millert Exp $
 .\"
-.Dd April 19, 1994
+.Dd December 8, 2002
 .Dt GETOPT 3
 .Os
 .Sh NAME
@@ -244,10 +244,20 @@ as an option flag.
 This practice is wrong, and should not be used in any current development.
 It is provided for backward compatibility
 .Em only .
+Care should be taken to not to use
+.Ql -
+as the first character in
+.Fa optstring
+to avoid a semantic conflict with
+.Tn GNU
+.Fn getopt ,
+which assigns different meaning to an
+.Fa optstring
+that begins with a
+.Ql - .
 By default, a single dash causes
 .Fn getopt
 to return \-1.
-This is, we believe, compatible with System V.
 .Pp
 It is also possible to handle digits as option letters.
 This allows