fix dune build

(dune seems to choke on some 4.08 features that were used in the Env
codebase already. It's not a bad idea to ensure that the compiler
codebase works well with 4.07.)

dune

@@ -51,7 +51,8 @@
    asttypes parsetree
 
    ;; TYPING
-   ident path primitive types btype oprint subst predef datarepr cmi_format env
+   ident path primitive types btype oprint subst predef datarepr
+   cmi_format persistent_env env
    typedtree printtyped ctype printtyp includeclass mtype envaux includecore
    typedtreeIter tast_mapper cmt_format untypeast includemod
    typetexp printpat parmatch stypes typedecl typeopt rec_check typecore

typing/env.ml

@@ -571,7 +571,6 @@ end = struct
   let is_name_of id =
     is (Ident.name id)
 end
-let _ = ignore Current_unit_name.is
 
 let set_unit_name = Current_unit_name.set
 let get_unit_name = Current_unit_name.get

typing/persistent_env.ml

@@ -107,7 +107,8 @@ let add_imported_opaque {imported_opaque_units; _} s =
 
 let find_in_cache {persistent_structures; _} s =
   match Hashtbl.find persistent_structures s with
-  | exception Not_found | Missing -> None
+  | exception Not_found -> None
+  | Missing -> None
   | Found (_ps, pm) -> Some pm
 
 let import_crcs penv ~source crcs =