shut up:
warning: using directive refers to implicitly-defined namespace 'std'

Index: config.h.in
--- config.h.in.orig
+++ config.h.in
@@ -317,6 +317,7 @@
 
 /* Namespace (on non-obj-c files) */
 #ifndef __IN_OBJC_FILE__
+#include <iosfwd>
 using namespace std;
 #define __STL_USE_NAMESPACES
 #endif