stl_threads.h (_Atomic_swap): Only enable path when platform supports __GTHREAD_MUTEX_INIT.

        * include/bits/stl_threads.h (_Atomic_swap): Only enable path
        when platform supports __GTHREAD_MUTEX_INIT.

From-SVN: r46725

libstdc++-v3/ChangeLog

+2001-11-02  Loren J. Rittle  <ljrittle@acm.org>
+
+	* include/bits/stl_threads.h (_Atomic_swap): Only enable path
+	when platform supports __GTHREAD_MUTEX_INIT.
+
 2001-11-02  Phil Edwards  <pme@gcc.gnu.org>
 
 	* acconfig.h:  Update comments.

libstdc++-v3/include/bits/stl_threads.h

@@ -196,7 +196,7 @@ struct _Refcount_Base
 // possibly concurrent updates use _Atomic_swap.
 // In some cases the operation is emulated with a lock.
 // GCC extension begin
-#ifdef __STL_GTHREADS
+#if defined (__STL_GTHREADS) && defined (__GTHREAD_MUTEX_INIT)
 // We don't provide an _Atomic_swap in this configuration.  This only
 // affects the use of ext/rope with threads.  Someone could add this
 // later, if required.  You can start by cloning the __STL_PTHREADS