Print "debug" when starting game compiled in debug mode.

src/standalone/main.cpp

@@ -48,6 +48,10 @@ int main() {
 		cloonel::ushort2(REFERENCE_WIDTH, REFERENCE_HEIGHT)
 	);
 
+#if !defined(NDEBUG)
+	std::cout << "Debug build\n";
+#endif
+
 	int ret_val = 0;
 	try {
 		sdl_main.Init();