Add a test that includes <complex.h> before mp11.hpp. Refs #88.

test/complex_h.cpp

@@ -0,0 +1,12 @@
+// Copyright 2023 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#define _SILENCE_CXX17_C_HEADER_DEPRECATION_WARNING
+
+#include <complex.h>
+#include <boost/mp11.hpp>
+
+int main()
+{
+}