Manually include compiled file in source via auto copy.

Author: JimBobSquarePants

src/Directory.Build.targets

@@ -55,17 +55,34 @@
   <ItemGroup>
     <!--Shared config files that have to exist at root level.-->
     <ConfigFilesToCopy Include="..\..\shared-infrastructure\.editorconfig;..\..\shared-infrastructure\.gitattributes" />
+    <!--
+    Copy submodule files generated via T4 templates.
+    We cannot include the generated files in the submodule as any solution wide T4 regeneration
+    could potentially cause the module to be marked dirty which is a headache.
+    This, instead, combined with using 'Compile Update' over 'Include' allows us to copy the file
+    across from the submodule and place it directly in the src folder for compilation.    
+    -->
+    <SubmoduleSourceFilesToCopy Include="..\..\shared-infrastructure\src\SharedInfrastructure\Guard.Numeric.cs" />
   </ItemGroup>
 
   <!--Ensures our config files are up to date.-->
   <Target Name="CopyFiles" BeforeTargets="Build">
-    <Copy SourceFiles="@(ConfigFilesToCopy)" DestinationFolder="..\..\" />
+    <Copy SourceFiles="@(ConfigFilesToCopy)"
+          SkipUnchangedFiles = "true"
+          DestinationFolder="..\..\" />
+    
+    <Copy SourceFiles="@(SubmoduleSourceFilesToCopy)"
+          DestinationFolder="..\..\src\ImageSharp\Common\Helpers"
+          SkipUnchangedFiles="true"
+          ContinueOnError="true" />
   </Target>
 
   <!-- Allows regenerating T4-generated files at build time using MsBuild -->
+  <!-- Enable on Windows OS to build all T4 templates. TODO: XPlat
   <Import Project="$(MSBuildExtensionsPath)\Microsoft\VisualStudio\v$(VisualStudioVersion)\TextTemplating\Microsoft.TextTemplating.targets" />
   <PropertyGroup>
     <TransformOnBuild>true</TransformOnBuild>
   </PropertyGroup>
+  -->
 
 </Project>