Building nuget-client inside the VMR fails on Windows

[ViktorHofer]

See https://dnceng.visualstudio.com/internal/_build/results?buildId=2437451&view=logs&j=9050e078-31bf-5111-d8ec-8b6fa95caf9c&t=4df1dbeb-294c-5d6e-97b8-581fe506c270 as an example.

  D:\a\_work\1\s\src\nuget-client\artifacts\sb\package-cache\microsoft.sourcelink.common\1.0.0\build\Microsoft.SourceLink.Common.targets(52,5): error : Source control information is not available - the generated source link is empty. [D:\a\_work\1\s\src\nuget-client\src\NuGet.Core\NuGet.Versioning\NuGet.Versioning.csproj::TargetFramework=netstandard2.0]
  D:\a\_work\1\s\src\nuget-client\artifacts\sb\package-cache\microsoft.sourcelink.common\1.0.0\build\Microsoft.SourceLink.Common.targets(52,5): error : Source control information is not available - the generated source link is empty. [D:\a\_work\1\s\src\nuget-client\src\NuGet.Core\NuGet.Frameworks\NuGet.Frameworks.csproj::TargetFramework=net472]
  D:\a\_work\1\s\src\nuget-client\artifacts\sb\package-cache\microsoft.sourcelink.common\1.0.0\build\Microsoft.SourceLink.Common.targets(52,5): error : Source control information is not available - the generated source link is empty. [D:\a\_work\1\s\src\nuget-client\src\NuGet.Core\NuGet.Versioning\NuGet.Versioning.csproj::TargetFramework=net472]
  D:\a\_work\1\s\src\nuget-client\artifacts\sb\package-cache\microsoft.sourcelink.common\1.0.0\build\Microsoft.SourceLink.Common.targets(52,5): error : Source control information is not available - the generated source link is empty. [D:\a\_work\1\s\src\nuget-client\src\NuGet.Core\NuGet.Frameworks\NuGet.Frameworks.csproj::TargetFramework=netstandard2.0]

Unsure why this doesn't fail in PR builds. This never worked in official builds and started failing in https://dnceng.visualstudio.com/internal/_build/results?buildId=2434049&view=results which contains the commit that enables building nuget-client in unified-build.

cc @mmitche

[ViktorHofer]

I also noticed that nuget-client uses that ancient 1.0.0 version of sourcelink and submitted NuGet/NuGet.Client#5764 to clean that up and not depend on sourcelink packages anymore.

[mmitche]

My guess is that there the use of the internal project and repo changes something subtle around sourcelink