Windows support by Ruben Van Boxem.

llvm-svn: 142235
diff --git a/libcxx/include/fstream b/libcxx/include/fstream
index 7034aab..b6a2ab0 100644
--- a/libcxx/include/fstream
+++ b/libcxx/include/fstream
@@ -171,7 +171,9 @@
 #include <__locale>
 #include <cstdio>
 
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #pragma GCC system_header
+#endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD