Verify new roslyn changes don't break us

- This tests a build of dotnet/roslyn#56341

Author: halter73

Directory.Build.props

@@ -110,7 +110,7 @@
   <!-- Warnings and errors -->
   <PropertyGroup>
     <!-- Ensure API docs are available. -->
-    <NoWarn>$(NoWarn.Replace('1591', ''))</NoWarn>
+    <NoWarn>$(NoWarn.Replace('1591', ''));NETSDK1023</NoWarn>
     <NoWarn Condition=" '$(BuildingInsideVisualStudio)' == 'true' ">$(NoWarn);0105</NoWarn>
 
     <!-- For local builds, don't make missing XML docs a fatal build error, but still surface so we have visibility into undocumented APIs. -->

Directory.Build.targets

@@ -191,4 +191,11 @@
   <Import Project="eng\targets\FunctionalTestAsset.targets" Condition="'$(IsTestAssetProject)' == 'true'" />
   <Import Project="eng\targets\FunctionalTestWithAssets.targets" Condition="'$(ContainsFunctionalTestAssets)' == 'true'" />
 
+  <ItemGroup>
+    <PackageReference Include="Microsoft.Net.Compilers.Toolset"
+      Version="4.0.0-ci.final"
+      PrivateAssets="all"
+      IsImplicitlyDefined="true" />
+  </ItemGroup>
+
 </Project>

NuGet.config

@@ -2,6 +2,7 @@
 <configuration>
   <packageSources>
     <clear />
+    <add key="local" value="./packages" />
     <add key="dotnet-eng" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet-eng/nuget/v3/index.json" />
     <add key="dotnet-tools" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet-tools/nuget/v3/index.json" />
     <add key="dotnet5" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet5/nuget/v3/index.json" />

eng/tools/GenerateFiles/Directory.Build.targets.in

@@ -54,6 +54,11 @@
           Condition=" '$(IsServicingBuild)' != 'true' ">${MicrosoftAspNetCoreAppRefVersion}</TargetingPackVersion>
     </KnownFrameworkReference>
 
+    <PackageReference Include="Microsoft.Net.Compilers.Toolset"
+      Version="4.0.0-ci.final"
+      PrivateAssets="all"
+      IsImplicitlyDefined="true" />
+
   </ItemGroup>
 
   <!-- Warn if the "just-built" ASP.NET Core shared framework does not exist. -->