sdk: New .csproj cannot reference GAC assemblies

From @jnm2 on March 13, 2017 20:31

You can no longer reference some GAC assemblies without specifying a HintPath, at which point there isn’t much point in using the GAC at all.

Class1.cs:

using System;
using Microsoft.SolverFoundation.Services;

public class Class1
{
    public static readonly Type X = typeof(ISolver);
}

Old .csproj, working:

<Project ToolsVersion="15.0">
  <Import Project="$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props" />
  <PropertyGroup>
    <OutputType>Library</OutputType>
    <TargetFrameworkVersion>v4.6.2</TargetFrameworkVersion>
    <OutputPath>bin\$(Configuration)\</OutputPath>
  </PropertyGroup>
  <ItemGroup>
    <Reference Include="Microsoft.Solver.Foundation" />
  </ItemGroup>
  <ItemGroup>
    <Compile Include="*.cs" />
  </ItemGroup>
  <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
</Project>

New .csproj fails to find the reference:

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <TargetFramework>net462</TargetFramework>
  </PropertyGroup>

  <ItemGroup>
    <Reference Include="Microsoft.Solver.Foundation" />
  </ItemGroup>

</Project>

This also does not work: <Reference Include="Microsoft.Solver.Foundation, Version=3.0.2.10889, Culture=neutral, PublicKeyToken=31bf3856ad364e35" />.

Why is this broken?

Copied from original issue: dotnet/roslyn-project-system#1739