Roslyn has no reference to System.Runtime

By request of Dejan in the comment section, I’ll post the answer (to my problem) as a real answer.

I’ve found out what the problem was! The compiler was correct all along. A blog post of smack0007 triggered me of trying something else. Instead of using the Facade dll, try referencing the necessary dll’s manually.
The GetGlobalReferences method now looks like this:

private IEnumerable<MetadataReference> GetGlobalReferences()
{
    var assemblies = new [] 
        {
            /*Making sure all MEF assemblies are loaded*/
            typeof(System.Composition.Convention.AttributedModelProvider).Assembly, //System.Composition.AttributeModel
            typeof(System.Composition.Convention.ConventionBuilder).Assembly,   //System.Composition.Convention
            typeof(System.Composition.Hosting.CompositionHost).Assembly,        //System.Composition.Hosting
            typeof(System.Composition.CompositionContext).Assembly,             //System.Composition.Runtime
            typeof(System.Composition.CompositionContextExtensions).Assembly,   //System.Composition.TypedParts

            /*Used for the GeneratedCode attribute*/
            typeof(System.CodeDom.Compiler.CodeCompiler).Assembly,              //System.CodeDom.Compiler
        };

    var refs = from a in assemblies 
                select new MetadataFileReference(a.Location);
    var returnList = refs.ToList();

    //The location of the .NET assemblies
    var assemblyPath = Path.GetDirectoryName(typeof(object).Assembly.Location);

    /* 
        * Adding some necessary .NET assemblies
        * These assemblies couldn't be loaded correctly via the same construction as above,
        * in specific the System.Runtime.
        */
    returnList.Add(new MetadataFileReference(Path.Combine(assemblyPath, "mscorlib.dll")));
    returnList.Add(new MetadataFileReference(Path.Combine(assemblyPath, "System.dll")));
    returnList.Add(new MetadataFileReference(Path.Combine(assemblyPath, "System.Core.dll")));
    returnList.Add(new MetadataFileReference(Path.Combine(assemblyPath, "System.Runtime.dll")));

    return returnList;
}

When decompiling the System.Runtime.dll I also saw why it couldn’t be referenced in any other way. The dll is empty, it only contains some references to other assemblies. Therefore one can’t reference this assembly in any other way.