Add tests that include <windows.h>

test/spinlock_windows_h_test.cpp

@@ -0,0 +1,11 @@
+// Copyright 2018 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+
+#if defined(_WIN32) || defined(__WIN32__) || defined(__CYGWIN__)
+# include <windows.h>
+# include <boost/smart_ptr/detail/spinlock.hpp>
+#endif
+
+int main()
+{
+}