Add deterministic C++ reference adapter

tests/fixtures/reference-cpp/include/config.hpp

@@ -0,0 +1,15 @@
+#pragma once
+
+#include "detail.hpp"
+
+namespace demo {
+
+struct Config {
+    int limit;
+};
+
+inline int effective_limit(const Config& config) {
+    return normalize(config.limit);
+}
+
+}  // namespace demo