Add mscorlib facade for refs consuming Windows.winmd

Reference assemblies consuming Windows.winmd need to have
an mscorlib facade because Windows.winmd has references to
types in mscorlib.

src/System.Runtime.WindowsRuntime/ref/System.Runtime.WindowsRuntime.csproj

@@ -22,6 +22,7 @@
   </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="..\..\..\external\winrt\winrt.depproj" />
+    <ProjectReference Include="..\..\mscorlib.WinRT-Facade\ref\mscorlib.WinRT-Facade.csproj" />
     <ProjectReference Include="..\..\System.Runtime\ref\System.Runtime.csproj" />
     <ProjectReference Include="..\..\System.Runtime.Extensions\ref\System.Runtime.Extensions.csproj" />
     <ProjectReference Include="..\..\System.IO\ref\System.IO.csproj" />

src/mscorlib.WinRT-Facade/ref/Configurations.props

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project ToolsVersion="14.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <PropertyGroup>
+    <BuildConfigurations>
+      uap;
+    </BuildConfigurations>
+  </PropertyGroup>
+</Project>

src/mscorlib.WinRT-Facade/ref/TypeForwards.cs

@@ -0,0 +1,33 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Runtime.CompilerServices;
+
+// The following types are can be referenced by windows.winmd and are spec'ed to come from mscorlib
+[assembly: TypeForwardedTo(typeof(System.Attribute))]
+[assembly: TypeForwardedTo(typeof(System.Boolean))]
+[assembly: TypeForwardedTo(typeof(System.Byte))]
+[assembly: TypeForwardedTo(typeof(System.Char))]
+[assembly: TypeForwardedTo(typeof(System.Double))]
+[assembly: TypeForwardedTo(typeof(System.Enum))]
+[assembly: TypeForwardedTo(typeof(System.FlagsAttribute))]
+[assembly: TypeForwardedTo(typeof(System.Guid))]
+[assembly: TypeForwardedTo(typeof(System.Int16))]
+[assembly: TypeForwardedTo(typeof(System.Int32))]
+[assembly: TypeForwardedTo(typeof(System.Int64))]
+[assembly: TypeForwardedTo(typeof(System.IntPtr))]
+[assembly: TypeForwardedTo(typeof(System.MulticastDelegate))]
+[assembly: TypeForwardedTo(typeof(System.Object))]
+[assembly: TypeForwardedTo(typeof(System.Runtime.CompilerServices.IsConst))]
+[assembly: TypeForwardedTo(typeof(System.Single))]
+[assembly: TypeForwardedTo(typeof(System.String))]
+[assembly: TypeForwardedTo(typeof(System.Type))]
+[assembly: TypeForwardedTo(typeof(System.UInt16))]
+[assembly: TypeForwardedTo(typeof(System.UInt32))]
+[assembly: TypeForwardedTo(typeof(System.UInt64))]
+[assembly: TypeForwardedTo(typeof(System.ValueType))]
+[assembly: TypeForwardedTo(typeof(void))] // System.Void
+
+// XAML compiler is checking for the following
+[assembly: TypeForwardedTo(typeof(System.Array))]

src/mscorlib.WinRT-Facade/ref/mscorlib.WinRT-Facade.csproj

@@ -0,0 +1,19 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project ToolsVersion="14.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <Import Project="$([MSBuild]::GetDirectoryNameOfFileAbove($(MSBuildThisFileDirectory), dir.props))\dir.props" />
+  <PropertyGroup>
+    <AssemblyName>mscorlib</AssemblyName>
+    <AssemblyVersion>4.0.0.0</AssemblyVersion>
+    <UseECMAKey>true</UseECMAKey>
+    <!-- do not binplace, this is only used to help compile references
+         against Windows.winmd.  The real mscorlib comes from src/shims/shims.proj -->
+    <BinPlaceRef>false</BinPlaceRef>
+  </PropertyGroup>
+  <ItemGroup>
+    <Compile Include="TypeForwards.cs" />
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\..\System.Runtime\ref\System.Runtime.csproj" />
+  </ItemGroup>
+  <Import Project="$([MSBuild]::GetDirectoryNameOfFileAbove($(MSBuildThisFileDirectory), dir.targets))\dir.targets" />
+</Project>