[release/3.1.1xx] Update dependencies from dotnet/toolset (#4797)

* Update dependencies from https://github.com/dotnet/toolset build 20190924.3

- Microsoft.Dotnet.Toolset.Internal - 3.1.100-preview1.19474.3

Dependency coherency updates

- Microsoft.NET.Sdk - 3.1.100-preview1.19463.2 (parent: Microsoft.Dotnet.Toolset.Internal)
- Microsoft.DotNet.MSBuildSdkResolver - 3.1.100-preview1.19474.2 (parent: Microsoft.Dotnet.Toolset.Internal)

* Override PATH to let razor find stage2 dotnet

test/EndToEnd/ProjectBuildTests.cs

@@ -143,10 +143,12 @@ namespace EndToEnd.Tests
                 .Execute(restoreArgs)
                 .Should().Pass();
 
+            var dotnetRoot = Path.GetDirectoryName(RepoDirectoriesProvider.DotnetUnderTest);
             new BuildCommand()
-                .WithWorkingDirectory(projectDirectory)
-                .Execute()
-                .Should().Pass();
+                 .WithEnvironmentVariable("PATH", dotnetRoot) // override PATH since razor rely on PATH to find dotnet
+                 .WithWorkingDirectory(projectDirectory)
+                 .Execute()
+                 .Should().Pass();
         }
     }
 }