[LITE][BUILD] fix clang compile armv8 cpu 's shared lib. test=develop (#3123)

* fix clang compile armv8 cpu 's shared lib. test=develop

* use build-in shared helper function. test=develop

lite/api/paddle_api.h

@@ -206,7 +206,7 @@ class LITE_API MobileConfig : public ConfigBase {
 };
 
 template <typename ConfigT>
-std::shared_ptr<PaddlePredictor> CreatePaddlePredictor(const ConfigT&);
+LITE_API std::shared_ptr<PaddlePredictor> CreatePaddlePredictor(const ConfigT&);
 
 }  // namespace lite_api
 }  // namespace paddle