revert a change

cpp/src/arrow/util/thread_pool.cc

@@ -674,10 +674,10 @@ Result<std::shared_ptr<ThreadPool>> ThreadPool::Make(int threads) {
 
 Result<std::shared_ptr<ThreadPool>> ThreadPool::MakeEternal(int threads) {
   ARROW_ASSIGN_OR_RAISE(auto pool, Make(threads));
-#  ifdef _WIN32
   // On Windows, the ThreadPool destructor may be called after non-main threads
   // have been killed by the OS, and hang in a condition variable.
   // On Unix, we want to avoid leak reports by Valgrind.
+#  ifdef _WIN32
   pool->shutdown_on_destroy_ = false;
 #  endif
   return pool;