add a signal to indicate if it has_warnings or not

Author: bobzhang

utils/warnings.ml

@@ -620,6 +620,7 @@ let sub_locs = function
       ]
   | _ -> []
 
+let has_warnings = ref false ;;  
 let nerrors = ref 0;;
 
 type reporting_information =
@@ -639,6 +640,7 @@ let report w =
   match is_active w with
   | false -> `Inactive
   | true ->
+     has_warnings := true; 
      if is_error w then incr nerrors;
      `Active { number = number w; message = message w; is_error = is_error w;
                sub_locs = sub_locs w;

utils/warnings.mli

@@ -134,6 +134,7 @@ val mk_lazy: (unit -> 'a) -> 'a Lazy.t
         the warning settings at the time [mk_lazy] is called. *)
 
 #if true then
+val has_warnings : bool ref
 val nerrors : int ref
 val message : t -> string 
 val number: t -> int