Disable repo prebuilt baseline during tarball builds (#14192)

Author: MichaelSimons

src/SourceBuild/tarball/content/ArcadeOverrides/AfterSourceBuild.proj

@@ -72,7 +72,8 @@
       OutputBaselineFile="$(SourceBuildSelfPrebuiltReportDir)generated-new-baseline.xml"
       OutputReportFile="$(SourceBuildSelfPrebuiltReportDir)baseline-comparison.xml"
       AllowTestProjectUsage="$(AllowTestProjectUsage)"
-      ContinueOnError="$(ContinueOnPrebuiltBaselineError)" />
+      ContinueOnError="$(ContinueOnPrebuiltBaselineError)"
+      Condition="'$(DotNetBuildFromSourceFlavor)' != 'Product'" />
   </Target>
 
   <!--

src/SourceBuild/tarball/content/repos/Directory.Build.props

@@ -45,6 +45,7 @@
 
   <ItemGroup>
     <EnvironmentVariables Include="DotNetBuildFromSource=true" />
+    <EnvironmentVariables Include="DotNetBuildFromSourceFlavor=Product" />
     <EnvironmentVariables Include="DotNetPackageVersionPropsPath=$(PackageVersionPropsPath)" />
     <EnvironmentVariables Include="DotNetRestorePackagesPath=$(PackagesDir)" />
     <EnvironmentVariables Include="DotNetBuildOffline=true" />