Update instructions for building runtime repo (#58172)

Co-authored-by: Charles Stoner <chucks@microsoft.com>

Author: jcouv

docs/contributing/Building, Debugging, and Testing on Windows.md

@@ -169,12 +169,12 @@ under `AppData`, not from `Program File`).
 
 ### Testing on the [dotnet/runtime](https://github.com/dotnet/runtime) repo
 
-1. make sure that you can build the `runtime` repo as baseline (run `build.cmd libs`, which should be sufficient to build all C# code, installing any prerequisites if prompted to)
+1. make sure that you can build the `runtime` repo as baseline (run `build.cmd libs+libs.tests`, which should be sufficient to build all C# code, installing any prerequisites if prompted to, and perhaps `git clean -xdf` and `build.cmd -restore` initially - see [runtime repo documentation](https://github.com/dotnet/runtime/blob/main/docs/workflow/README.md) for specific prerequisites and build instructions)
 2. `build.cmd -pack` on your `roslyn` repo
 3. in `%userprofile%\.nuget\packages\microsoft.net.compilers.toolset` delete the version of the toolset that you just packed so that the new one will get put into the cache
 4. modify your local enlistment of `runtime` as illustrated in [this commit](https://github.com/RikkiGibson/runtime/commit/da3c6d96c3764e571269b07650a374678b476384) then build again
     - add `<RestoreAdditionalProjectSources><PATH-TO-YOUR-ROSLYN-ENLISTMENT>\artifacts\packages\Debug\Shipping\</RestoreAdditionalProjectSources>` using the local path to your `roslyn` repo to `Directory.Build.props`
-    - add `<MicrosoftNetCompilersToolsetVersion>3.9.0-dev</MicrosoftNetCompilersToolsetVersion>` with the package version you just packed (look in above artifacts folder) to `eng/Versions.props`
+    - add `<UsingToolMicrosoftNetCompilers>true</UsingToolMicrosoftNetCompilers>` and `<MicrosoftNetCompilersToolsetVersion>4.1.0-dev</MicrosoftNetCompilersToolsetVersion>` with the package version you just packed (look in above artifacts folder) to `eng/Versions.props`
 
 ### Testing with extra IOperation validation