Using Studio's “Custom Tool” in MSBuild

<!-- the template -->
<None Include="Template.in">
  <Generator>Template Processor</Generator>
  <LastGenOutput>Template.in.Designer.cs</LastGenOutput>
</None>
<!-- generated file -->
<Compile Include="Template.in.Designer.cs">
  <AutoGen>True</AutoGen>
  <DesignTime>True</DesignTime>
  <DependentUpon>Template.in</DependentUpon>
</Compile>