Windows support by Ruben Van Boxem.

llvm-svn: 142235
diff --git a/libcxx/include/cstdlib b/libcxx/include/cstdlib
index 26c27ff..e8726cf 100644
--- a/libcxx/include/cstdlib
+++ b/libcxx/include/cstdlib
@@ -82,7 +82,9 @@
 #include <__config>
 #include <stdlib.h>
 
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #pragma GCC system_header
+#endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD