Workaround for build issue: use xcopy to copy System.Waf.Uwp.xr.xml into the correct folder

Author: jbe2277

src/System.Waf/System.Waf/System.Waf.Uwp/System.Waf.Uwp.csproj

@@ -82,10 +82,12 @@
     <Page Include="Themes\Generic.xaml">
       <SubType>Designer</SubType>
       <Generator>MSBuild:Compile</Generator>
-      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
     </Page>
   </ItemGroup>
   <Import Project="$(MSBuildExtensionsPath)\Microsoft\WindowsXaml\v$(VisualStudioVersion)\Microsoft.Windows.UI.Xaml.CSharp.targets" />
+  <PropertyGroup>
+    <PostBuildEvent>xcopy "$(TargetDir)System.Waf.Uwp.xr.xml" "$(TargetDir)System.Waf.Uwp\"</PostBuildEvent>
+  </PropertyGroup>
   <!-- To modify your build process, add your task inside one of the targets below and uncomment it. 
        Other similar extension points exist, see Microsoft.Common.targets.
   <Target Name="BeforeBuild">