Windows support by Ruben Van Boxem.

llvm-svn: 142235
diff --git a/libcxx/include/regex b/libcxx/include/regex
index 760f4eb..048fbef 100644
--- a/libcxx/include/regex
+++ b/libcxx/include/regex
@@ -732,7 +732,9 @@
 #include <vector>
 #include <deque>
 
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #pragma GCC system_header
+#endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD