Index: libcxx/include/__support/ibm/xlocale.h
===================================================================
--- libcxx/include/__support/ibm/xlocale.h
+++ libcxx/include/__support/ibm/xlocale.h
@@ -310,7 +310,11 @@
   }
 
   va_list ap_copy;
+#if defined(_LIBCPP_CXX03_LANG) && defined(__va_copy)
+  __va_copy(ap_copy, ap);
+#else
   va_copy(ap_copy, ap);
+#endif
   int str_size = vsnprintf(*strp, buff_size, fmt,  ap_copy);
   va_end(ap_copy);