Add test/cmake_subdir_test

test/cmake_subdir_test/main.cpp

@@ -0,0 +1,25 @@
+//  Copyright 2026 Peter Dimov
+//  Distributed under the Boost Software License, Version 1.0.
+//  http://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/xpressive/xpressive.hpp>
+#include <string>
+
+using namespace boost::xpressive;
+
+int main()
+{
+    std::string hello( "hello world!" );
+
+    sregex rex = sregex::compile( "(\\w+) (\\w+)!" );
+    smatch what;
+
+    if( regex_match( hello, what, rex ) )
+    {
+        return what.size() == 3? 0: 1;
+    }
+    else
+    {
+        return 2;
+    }
+}