Add cmake_install_test, cmake_subdir_test

test/cmake_subdir_test/main.cpp

@@ -0,0 +1,10 @@
+// Copyright 2024 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/mpl/assert.hpp>
+
+int main()
+{
+    BOOST_MPL_ASSERT_RELATION( 1, <, 5 );
+}