Use atomic "mkdir -p" to create the directory "output".

generator/main.ml

@@ -72,7 +72,7 @@ let _ =
    let debugdir = Filename.concat dirname "output" in
    let debugdirBase = Filename.concat debugdir (String.capitalize basename) in
    (*  FAILURE ON WINDOWS   *)
-   let cmd = Printf.sprintf "test -d %s || mkdir %s" debugdir debugdir in
+   let cmd = Printf.sprintf "mkdir -p %s" debugdir in
    begin try ignore (Sys.command cmd)
          with _ -> Printf.printf "Could not create debug directory\n" end;