Merge in 'release/2.1' changes

Author: dotnet-bot

build.proj

@@ -36,7 +36,7 @@
 
   <Target Name="RestoreOptData" Condition="'$(RestoreDuringBuild)'=='true' and '$(BuildType)'=='Release'">
     <PropertyGroup>
-      <_OptimizationDataFeed Condition="'$(DotNetBuildOffline)' != 'true'">--source https://dotnet.myget.org/F/dotnet-core-optimization-data/api/v3/index.json</_OptimizationDataFeed>
+      <_OptimizationDataFeed Condition="'$(DotNetBuildOffline)' != 'true'">--source https://pkgs.dev.azure.com/dnceng/public/_packaging/myget-legacy/nuget/v3/index.json</_OptimizationDataFeed>
     </PropertyGroup>
 
     <Exec Command="$(DotnetRestoreCommand) $(_OptimizationDataFeed) $(SourceDir).nuget/optdata/optdata.csproj"