libstdc++: Only use __gthread_yield if gthreads is available

libstdc++-v3/ChangeLog:

	* include/std/mutex (__lock_impl): Check
	_GLIBCXX_HAS_GTHREADS before using __gthread_yield.

diff --git a/libstdc++-v3/include/std/mutex b/libstdc++-v3/include/std/mutex
index eeb51fdb840e4f0fc8d76094f03eac188adf4b6a..7ab4ee126905e1424e18edfcff8e09ac41bfe63b 100644 (file)
--- a/libstdc++-v3/include/std/mutex
+++ b/libstdc++-v3/include/std/mutex
@@ -618,7 +618,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
                      return;
                    }
                }
-#ifdef _GLIBCXX_USE_SCHED_YIELD
+#if defined _GLIBCXX_HAS_GTHREADS && defined _GLIBCXX_USE_SCHED_YIELD
                __gthread_yield();
 #endif
                constexpr auto __n = 1 + sizeof...(_L1);