[ArPow] Update SBRP to get version with updated ilasm (#11233)

* Update SBRP to get version with updated ilasm

Also, remove the prebuilts for packages that weren't being built
correctly.

* Add empty prebuilt directory

eng/SourceBuild.Version.Details.xml

@@ -79,9 +79,9 @@
       <Sha>3fb25b8db3bec654e37e71a5b2b7fde14444bc2f</Sha>
       <SourceBuild RepoName="source-build" ManagedOnly="true" />
     </Dependency>
-    <Dependency Name="Microsoft.SourceBuild.Intermediate.source-build-reference-packages" Version="6.0.0-alpha.1.21359.1">
+    <Dependency Name="Microsoft.SourceBuild.Intermediate.source-build-reference-packages" Version="6.0.0-alpha.1.21373.1">
       <Uri>https://github.com/dotnet/source-build-reference-packages</Uri>
-      <Sha>8cfb504dabb5881e5bb22b36035ecc72d7426fdd</Sha>
+      <Sha>dfcca1bbae6e87df7b99bd7837410d9815f7a813</Sha>
       <SourceBuild RepoName="source-build-reference-packages" ManagedOnly="true" />
     </Dependency>
     <Dependency Name="XliffTasks" Version="1.0.0-beta.21325.1" CoherentParentDependency="Microsoft.DotNet.Arcade.Sdk">

src/SourceBuild/Arcade/tools/SourceBuildArcadeTarball.targets

@@ -203,6 +203,8 @@
       File="$(ArchiveArtifactsTextFile)"
       Lines="@(ArtifactUrls)"
       Overwrite="true" />
+
+    <MakeDir Directories="$(TarballRootDir)packages/prebuilt" />
   </Target>
 
 </Project>