Mark symbols that should be public (#18802)

shell/platform/linux/fl_method_call.cc

@@ -74,9 +74,9 @@ G_MODULE_EXPORT FlValue* fl_method_call_get_args(FlMethodCall* self) {
   return self->args;
 }
 
-gboolean fl_method_call_respond(FlMethodCall* self,
-                                FlMethodResponse* response,
-                                GError** error) {
+G_MODULE_EXPORT gboolean fl_method_call_respond(FlMethodCall* self,
+                                                FlMethodResponse* response,
+                                                GError** error) {
   g_return_val_if_fail(FL_IS_METHOD_CALL(self), FALSE);
   g_return_val_if_fail(FL_IS_METHOD_RESPONSE(response), FALSE);
   return fl_method_channel_respond(self->channel, self->response_handle,

shell/platform/linux/fl_method_response.cc

@@ -26,6 +26,9 @@ struct _FlMethodNotImplementedResponse {
   FlMethodResponse parent_instance;
 };
 
+// Added here to stop the compiler from optimising this function away.
+G_MODULE_EXPORT GType fl_method_response_get_type();
+
 G_DEFINE_TYPE(FlMethodResponse, fl_method_response, G_TYPE_OBJECT)
 G_DEFINE_TYPE(FlMethodSuccessResponse,
               fl_method_success_response,

shell/platform/linux/fl_plugin_registrar.cc

@@ -17,6 +17,9 @@ struct _FlPluginRegistrar {
   FlBinaryMessenger* messenger;
 };
 
+// Added here to stop the compiler from optimising this function away.
+G_MODULE_EXPORT GType fl_plugin_registrar_get_type();
+
 G_DEFINE_TYPE(FlPluginRegistrar, fl_plugin_registrar, G_TYPE_OBJECT)
 
 static void view_weak_notify_cb(gpointer user_data, GObject* object) {