Try pos args left to right when parsing command line

This doesn't affect how arguments are evaluated as each pos arg parse
only looks at the own range of argv but it does affect which arg's
completion is going to be used.

src/cmdliner_cline.ml

@@ -39,7 +39,7 @@ let arg_info_indexes args =
      their arg_info, a list with all arg_info for positional arguments and
      a cmdline mapping each arg_info to an empty [arg]. *)
   let rec loop optidx posidx cl = function
-  | [] -> optidx, posidx, cl
+  | [] -> optidx, List.rev posidx, cl
   | a :: l ->
       match Cmdliner_info.Arg.is_pos a with
       | true -> loop optidx (a :: posidx) (Amap.add a (P []) cl) l