Windows support by Ruben Van Boxem.

llvm-svn: 142235
diff --git a/libcxx/include/__std_stream b/libcxx/include/__std_stream
index 6ab0fd6..6df6556 100644
--- a/libcxx/include/__std_stream
+++ b/libcxx/include/__std_stream
@@ -17,7 +17,9 @@
 #include <__locale>
 #include <cstdio>
 
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #pragma GCC system_header
+#endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD