export explicitly from the test build's types module

tests/types.module.scm

@@ -1,3 +1,14 @@
 (module types
-    *
+    (add-struct
+     add-union
+     add-enum
+     add-typedef
+     add-define
+
+     type-match
+     map-fields
+
+     get-type-info
+     get-fields
+     get-underlying-type)
   "../types.scm")