fix corner case in collapse_vars (#5390)

fixes #5389

lib/ast.js

@@ -851,6 +851,9 @@ var AST_DefClass = DEFNODE("DefClass", null, {
     $propdoc: {
         name: "[AST_SymbolDefClass] the name of this class",
     },
+    resolve: function(def_class) {
+        return def_class ? this : this.parent_scope.resolve();
+    },
     _validate: function() {
         if (!(this.name instanceof AST_SymbolDefClass)) throw new Error("name must be AST_SymbolDefClass");
     },

lib/compress.js

@@ -3269,7 +3269,7 @@ Compressor.prototype.compress = function(node) {
                 if (def.scope.resolve() !== scope) return true;
                 if (modify_toplevel && compressor.exposed(def)) return true;
                 return !all(def.references, function(ref) {
-                    return ref.scope.resolve() === scope;
+                    return ref.scope.resolve(true) === scope;
                 });
             }