On server, channel dprint through the readline-device. Also some refactors and quality improvements.

luprex/cpp/drv/drvutil.cpp

@@ -354,4 +354,17 @@ std::string package_lua_source(const std::filesystem::path &base, std::ostream *
 }
 
 
-} // namespace drv
+} // namespace drvutil
+
+
+// Include the system-dependent part of drvutil.
+
+#if defined(__linux__)
+    #include "drvutil-linux.cpp"
+#elif  defined(_WIN32)
+    #include "drvutil-windows.cpp"
+#else
+    #error "Only support __linux__ or _WIN32"
+#endif
+
+