WiX: package the experimental runtime builds

This packages the experimental runtime builds to allow us to statically
link against the standard library. This will be used to allow us to
bootstrap the early swift-driver on Windows.

Author: compnerd

platforms/Windows/platforms/windows/windows.wixproj

@@ -10,9 +10,14 @@
       IncludeARM64=$(WindowsArchitectures.Contains("aarch64"));
       IncludeX64=$(WindowsArchitectures.Contains("x86_64"));
       IncludeX86=$(WindowsArchitectures.Contains("i686"));
+      IncludeExperimentalSDK=$(IncludeExperimentalSDK);
     </DefineConstants>
   </PropertyGroup>
 
+  <PropertyGroup Condition=" '$(IncludeExperimentalSDK)' == '' ">
+    <IncludeExperimentalSDK>False</IncludeExperimentalSDK>
+  </PropertyGroup>
+
   <ItemGroup>
     <PackageReference Include="WixToolset.Heat" Version="4.0.5" />
   </ItemGroup>