Fix workaround for Sun Studio compilers and message queue when compiling with threads.

This commit was SVN r19528.

ompi/debuggers/ompi_msgq_dll.c

@@ -149,6 +149,9 @@ opal_condition_t ompi_request_cond;
 size_t ompi_request_waiting;
 opal_mutex_t ompi_request_lock;
 opal_mutex_t opal_event_lock;
+#if OMPI_HAVE_THREAD_SUPPORT
+volatile
+#endif
 uint32_t opal_progress_recursion_depth_counter;
 int opal_progress_spin_count;
 volatile int32_t opal_progress_thread_count;