libstdc++: Fix errors when syncbuf is used without RTTI

libstdc++-v3/ChangeLog:

	* include/std/ostream (__syncbuf_base::_S_get): Mark parameter
	as unused and only use dynamic_cast when RTTI is enabled.

diff --git a/libstdc++-v3/include/std/ostream b/libstdc++-v3/include/std/ostream
index 85ed47e..c7c4e78 100644 (file)
--- a/libstdc++-v3/include/std/ostream
+++ b/libstdc++-v3/include/std/ostream
@@ -783,10 +783,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     {
     public:
       static bool*
-      _S_get(basic_streambuf<_CharT, _Traits>* __buf) noexcept
+      _S_get(basic_streambuf<_CharT, _Traits>* __buf [[maybe_unused]]) noexcept
       {
+#if __cpp_rtti
        if (auto __p = dynamic_cast<__syncbuf_base*>(__buf))
          return &__p->_M_emit_on_sync;
+#endif
        return nullptr;
       }