Add networking build script

Source/Engine/Engine/Engine.Build.cs

@@ -25,6 +25,7 @@ public class Engine : EngineModule
         options.PublicDependencies.Add("Input");
         options.PublicDependencies.Add("Level");
         options.PublicDependencies.Add("Navigation");
+        options.PublicDependencies.Add("Networking");
         options.PublicDependencies.Add("Physics");
         options.PublicDependencies.Add("Particles");
         options.PublicDependencies.Add("Scripting");

Source/Engine/Networking/Networking.Build.cs

@@ -0,0 +1,18 @@
+// Copyright (c) 2012-2021 Wojciech Figat. All rights reserved.
+
+using Flax.Build;
+using Flax.Build.NativeCpp;
+
+/// <summary>
+/// Networking module.
+/// </summary>
+public class Networking : EngineModule
+{
+    /// <inheritdoc />
+    public override void Setup(BuildOptions options)
+    {
+        base.Setup(options);
+
+        options.PublicDefinitions.Add("COMPILE_WITH_NETWORKING");
+    }
+}