fix(extern): 原地更新 export_extern_funcs

translator 与 LlvmGen 共享同一 dict 引用；替换属性导致 Gen 仍指向旧空 dict。改为 clear+update，确保跨模块 extern 裸名生效。

lib/Projectrans/Phase2Translator.py

@@ -2405,7 +2405,8 @@ class Phase2Translator:
                             _combined_extern[_node.name] = _sha1_key
                 except Exception:
                     continue
-            trans.translator._export_extern_funcs = _combined_extern
+            trans.translator._export_extern_funcs.clear()
+            trans.translator._export_extern_funcs.update(_combined_extern)
             if self._shared_generic_class_templates:
                 if not hasattr(trans.translator.ClassHandler, '_generic_class_templates'):
                     trans.translator.ClassHandler._generic_class_templates = {}
@@ -2427,7 +2428,7 @@ class Phase2Translator:
                         raise
                     _vlog().warning(f"收集导出外部函数声明失败: {_e}", "Exception")
             if export_extern_funcs:
-                trans.translator._export_extern_funcs = export_extern_funcs
+                trans.translator._export_extern_funcs.update(export_extern_funcs)
 
             for includes_dir in self.include_dirs:
                 if os.path.isdir(includes_dir):