anchor.diff:      /// Get the path to the .NET Framework implementation assemblies by using ToolLocationHelper.GetPathToDotNetFramework.
       /// This is only used to specify the "last resort" path for assembly resolution.
       let GetPathToDotNetFrameworkImlpementationAssemblies(v) =
  -#if FX_ATLEAST_45
           let v =
               match v with
               | Net11 ->  Some TargetDotNetFrameworkVersion.Version11
  
positive.code:             | null -> []
              | x -> [x]
          | _ -> []
  #else
          // FX_ATLEAST_45 is not defined for step when we build compiler with proto compiler.
          ignore v
          []
  #endif        
  
      let GetPathToDotNetFrameworkReferenceAssembliesFor40Plus(version) = 
  #if FX_ATLEAST_45
          // starting with .Net 4.0, the runtime dirs (WindowsFramework) are never used by MSBuild RAR
          let v =
              match version with
  
negative.code:             | null -> []
              | x -> [x]
          | None -> []        
  
      /// Use MSBuild to determine the version of the highest installed framework.
      let HighestInstalledNetFrameworkVersionMajorMinor() =
          if box (ToolLocationHelper.GetPathToDotNetFramework(TargetDotNetFrameworkVersion.Version461)) <> null then 4, Net461
          elif box (ToolLocationHelper.GetPathToDotNetFramework(TargetDotNetFrameworkVersion.Version46)) <> null then 4, Net46
          // 4.5.2 enumeration is not available in Dev15 MSBuild version
  