Windows support by Ruben Van Boxem.

llvm-svn: 142235
diff --git a/libcxx/include/algorithm b/libcxx/include/algorithm
index d6906a2..3a47b8d 100644
--- a/libcxx/include/algorithm
+++ b/libcxx/include/algorithm
@@ -595,7 +595,9 @@
 #include <iterator>
 #include <cstdlib>
 
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #pragma GCC system_header
+#endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD