[16.6 regression] Legacy project files that reference an SDK are not loading/building

**Visual Studio Version**: 16.6.0

**Summary**:
Updating Visual Studio from version 16.5.5 to 16.6.0 broke my legacy (non SDK-style) projects that reference the SDK [DasMulli.AssemblyInfoGeneration.Sdk](https://github.com/dasMulli/AssemblyInfoGenerationSdk).

**Steps to Reproduce**:
1. Create a new .NET Framework console application.
2. Delete the AssemblyInfo.cs file.
3. Close the solution.
4. Add the line `` to the project file (as the first line inside the `` tag).
5. Open the solution.
6. Try to build.

**Expected Behavior**:
The project should open and build without errors.

**Actual Behavior**:
At step 5: Visual Studio shows an yellow error bar that says it had errors loading the project. Here is the error that is shown if you click on "Open log file":

Error

```
25.05.2020 09:32:34
Recoverable
System.AggregateException: Project system data flow 'DataflowBlockSlim (ActionBlockSlimAsync`1 : 24683675)' closed because of an exception: System.AggregateException: One or more errors occurred. ---> System.ArgumentException: The project configuration "Debug|AnyCPU" was not found in the project manifest.
at Microsoft.Requires.Fail(String message)
at Microsoft.Requires.Fail(String unformattedMessage, Object[] args)
at Microsoft.VisualStudio.ProjectSystem.DefaultingProjectConfigurationsServiceBase.d__3.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.VisualStudio.ProjectSystem.VS.Implementation.VSUnconfiguredProjectIntegrationService.d__58.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.VisualStudio.ProjectSystem.VS.Implementation.VSUnconfiguredProjectIntegrationService.d__53.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.VisualStudio.ProjectSystem.VS.Tree.Dependencies.Subscriptions.DependenciesSnapshotProvider.ContextTracker.d__9.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.VisualStudio.ProjectSystem.VS.Tree.Dependencies.Subscriptions.DependenciesSnapshotProvider.<b__38_0>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.VisualStudio.Threading.SemaphoreSlimExtensions.d__1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.VisualStudio.ProjectSystem.VS.Tree.Dependencies.Subscriptions.DependenciesSnapshotProvider.<g__OnActiveConfiguredProjectEvaluatedAsync|30_1>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.VisualStudio.ProjectSystem.DataReceivingBlockSlim`1.d__5.MoveNext()
--- End of inner exception stack trace ---
---> (Inner Exception #0) System.ArgumentException: The project configuration "Debug|AnyCPU" was not found in the project manifest.
at Microsoft.Requires.Fail(String message)
at Microsoft.Requires.Fail(String unformattedMessage, Object[] args)
at Microsoft.VisualStudio.ProjectSystem.DefaultingProjectConfigurationsServiceBase.d__3.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.VisualStudio.ProjectSystem.VS.Implementation.VSUnconfiguredProjectIntegrationService.d__58.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.VisualStudio.ProjectSystem.VS.Implementation.VSUnconfiguredProjectIntegrationService.d__53.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.VisualStudio.ProjectSystem.VS.Tree.Dependencies.Subscriptions.DependenciesSnapshotProvider.ContextTracker.d__9.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.VisualStudio.ProjectSystem.VS.Tree.Dependencies.Subscriptions.DependenciesSnapshotProvider.<b__38_0>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.VisualStudio.Threading.SemaphoreSlimExtensions.d__1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.VisualStudio.ProjectSystem.VS.Tree.Dependencies.Subscriptions.DependenciesSnapshotProvider.<g__OnActiveConfiguredProjectEvaluatedAsync|30_1>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.VisualStudio.ProjectSystem.DataReceivingBlockSlim`1.d__5.MoveNext()<---
. ---> System.ArgumentException: The project configuration "Debug|AnyCPU" was not found in the project manifest.
at Microsoft.Requires.Fail(String message)
at Microsoft.Requires.Fail(String unformattedMessage, Object[] args)
at Microsoft.VisualStudio.ProjectSystem.DefaultingProjectConfigurationsServiceBase.d__3.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.VisualStudio.ProjectSystem.VS.Implementation.VSUnconfiguredProjectIntegrationService.d__58.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.VisualStudio.ProjectSystem.VS.Implementation.VSUnconfiguredProjectIntegrationService.d__53.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.VisualStudio.ProjectSystem.VS.Tree.Dependencies.Subscriptions.DependenciesSnapshotProvider.ContextTracker.d__9.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.VisualStudio.ProjectSystem.VS.Tree.Dependencies.Subscriptions.DependenciesSnapshotProvider.<b__38_0>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.VisualStudio.Threading.SemaphoreSlimExtensions.d__1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.VisualStudio.ProjectSystem.VS.Tree.Dependencies.Subscriptions.DependenciesSnapshotProvider.<g__OnActiveConfiguredProjectEvaluatedAsync|30_1>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.VisualStudio.ProjectSystem.DataReceivingBlockSlim`1.d__5.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at Microsoft.VisualStudio.ProjectSystem.CommonProjectSystemTools.Rethrow(Exception ex)
at Microsoft.VisualStudio.ProjectSystem.ProjectErrorReporting.<>c__DisplayClass6_0.b__0()
at Microsoft.VisualStudio.ProjectSystem.ExceptionFilter.<>c__DisplayClass2_0.g__action|0()
at GuardMethodClass.GuardMethod(Func`1 , Func`2 , Func`2 )
--- End of inner exception stack trace ---
---> (Inner Exception #0) System.ArgumentException: The project configuration "Debug|AnyCPU" was not found in the project manifest.
at Microsoft.Requires.Fail(String message)
at Microsoft.Requires.Fail(String unformattedMessage, Object[] args)
at Microsoft.VisualStudio.ProjectSystem.DefaultingProjectConfigurationsServiceBase.d__3.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.VisualStudio.ProjectSystem.VS.Implementation.VSUnconfiguredProjectIntegrationService.d__58.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.VisualStudio.ProjectSystem.VS.Implementation.VSUnconfiguredProjectIntegrationService.d__53.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.VisualStudio.ProjectSystem.VS.Tree.Dependencies.Subscriptions.DependenciesSnapshotProvider.ContextTracker.d__9.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.VisualStudio.ProjectSystem.VS.Tree.Dependencies.Subscriptions.DependenciesSnapshotProvider.<b__38_0>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.VisualStudio.Threading.SemaphoreSlimExtensions.d__1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.VisualStudio.ProjectSystem.VS.Tree.Dependencies.Subscriptions.DependenciesSnapshotProvider.<g__OnActiveConfiguredProjectEvaluatedAsync|30_1>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.VisualStudio.ProjectSystem.DataReceivingBlockSlim`1.d__5.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at Microsoft.VisualStudio.ProjectSystem.CommonProjectSystemTools.Rethrow(Exception ex)
at Microsoft.VisualStudio.ProjectSystem.ProjectErrorReporting.<>c__DisplayClass6_0.b__0()
at Microsoft.VisualStudio.ProjectSystem.ExceptionFilter.<>c__DisplayClass2_0.g__action|0()
at GuardMethodClass.GuardMethod(Func`1 , Func`2 , Func`2 )<---

```

At step 6: There is either no option at all to build the project, or the project will be skipped in the build.

**User Impact**:
Unable to build certain solutions after updating to Visual Studio version 16.6.0

**Additional Information**:
It seems like a partial workaround is to add this to the project file:

```

Debug;Release
AnyCPU

```

But this only helps as long as the project doesn't reference any NuGet packages via a `` tag in the project file. As soon as it does, the build is broken again because the NuGet package restore doesn't work any more.