[X11] Reference X11 backend from ControlCatalog

samples/ControlCatalog.NetCore/ControlCatalog.NetCore.csproj

@@ -8,6 +8,7 @@
   <ItemGroup>
     <ProjectReference Include="..\..\src\Avalonia.DesignerSupport\Avalonia.DesignerSupport.csproj" />
     <ProjectReference Include="..\..\src\Avalonia.DotNetCoreRuntime\Avalonia.DotNetCoreRuntime.csproj" />
+    <ProjectReference Include="..\..\src\Avalonia.X11\Avalonia.X11.csproj" />
     <ProjectReference Include="..\..\src\Linux\Avalonia.LinuxFramebuffer\Avalonia.LinuxFramebuffer.csproj" />
     <ProjectReference Include="..\ControlCatalog\ControlCatalog.csproj" />
   </ItemGroup>