By default, VBRuntime is chosen as follows:

    .NET Framework:
      Same as classic vbproj. $(FrameworkPathOverride) is passed  as
      /sdkpath to compiler and Microsoft.VisualBasic.dll will be used
      from there even if there is no explicit reference to it. This is
      accomplished by leaving $(VBRuntime) unset.

    .NET Core 3.0+:
      Locate Microsoft.VisualBasic among references and pass it as
      /vbruntime to compiler.

    .NET Core < 3.0 or .NET Standard:
      Use embedded VB runtime as there is no Microsoft.VisualBasic.dll
      available that is complete enough to serve as /vbruntime.

   These defaults can be overridden as follows:

    $(UseReferencedVBRuntime) == true:
      Use referenced Microsoft.VisualBasic regardless of TFM.

      This is an escape hatch for a custom Microsoft.VisualBasic reference
      that can work as /vbruntime on a target framework other than .NET Core 3.0+

    $(VBRuntime) != '':
      Pass it through to compiler unchanged.