Set prebuilt report dir even though it won't be in the nupkg (#15302)

Author: mmitche

src/Microsoft.DotNet.Arcade.Sdk/tools/SourceBuild/SourceBuildArcade.targets

@@ -34,7 +34,8 @@
     <CurrentRepoSourceBuildSourceDir>$([MSBuild]::NormalizeDirectory('$(SourceBuildOutputDir)', 'src'))</CurrentRepoSourceBuildSourceDir>
     <CurrentRepoSourceBuildSourceDir Condition="'$(UseInnerClone)' != 'true'">$(RepoRoot)</CurrentRepoSourceBuildSourceDir>
     <CurrentRepoSourceBuildPackageCache>$([MSBuild]::NormalizeDirectory('$(SourceBuildOutputDir)', 'package-cache'))</CurrentRepoSourceBuildPackageCache>
-
+    <SourceBuildSelfPrebuiltReportDir>$([MSBuild]::NormalizeDirectory('$(SourceBuildOutputDir)', 'prebuilt-report'))</SourceBuildSelfPrebuiltReportDir>
+    
     <!--
       Keep artifacts/ inside source dir so that ancestor-based file lookups find the inner repo, not
       the outer repo. The inner repo global.json and NuGet.config files may have been modified by