[cil_types_debug] remove dependency on Cil_datatype

The transitive dependencies are just to heavy to load in ocamldebug

src/kernel_services/ast_printing/cil_types_debug.ml

@@ -607,7 +607,8 @@ and pp_location fmt (pos_start,pos_end) =
   p fmt "(%a,%a)" pp_filepath_position pos_start pp_filepath_position pos_end
 
 and pp_if_loc_known prefix suffix fmt loc =
-  if print_locations && loc <> Cil_datatype.Location.unknown
+  if print_locations &&
+     not (Filepath.Normalized.is_unknown (fst loc).Filepath.pos_path)
   then Format.fprintf fmt "%s%a%s" prefix pp_location loc suffix
   else ()