This is presumably not meant to be exported

Change-Id: Id11393c44ddd217d3def259ea5a8df9f8bb27711

comphelper/source/misc/threadpool.cxx

@@ -27,7 +27,7 @@ static thread_local bool gbIsWorkerThread;
 #endif
 
 // used to group thread-tasks for waiting in waitTillDone()
-class COMPHELPER_DLLPUBLIC ThreadTaskTag
+class ThreadTaskTag
 {
     std::mutex maMutex;
     sal_Int32 mnTasksWorking;