Crash with default as C

[jcouv]

It's probably good to also test default as T where T is an open type.

	at System.Diagnostics.Debug.Assert(Boolean condition)
	Binder\Binder_Operators.cs(3035,0): at Microsoft.CodeAnalysis.CSharp.Binder.BindAsOperator(BinaryExpressionSyntax node, DiagnosticBag diagnostics)
	Binder\Binder_Expressions.cs(510,0): at Microsoft.CodeAnalysis.CSharp.Binder.BindExpressionInternal(ExpressionSyntax node, DiagnosticBag diagnostics, Boolean invoked, Boolean indexed)
	Binder\Binder_Expressions.cs(414,0): at Microsoft.CodeAnalysis.CSharp.Binder.BindExpressionAllowArgList(ExpressionSyntax node, DiagnosticBag diagnostics)
	Binder\Binder_Expressions.cs(310,0): at Microsoft.CodeAnalysis.CSharp.Binder.BindValueAllowArgList(ExpressionSyntax node, DiagnosticBag diagnostics, BindValueKind valueKind)
	Binder\Binder_Expressions.cs(2202,0): at Microsoft.CodeAnalysis.CSharp.Binder.BindArgumentExpression(DiagnosticBag diagnostics, ExpressionSyntax argumentExpression, RefKind refKind, Boolean allowArglist)
	Binder\Binder_Expressions.cs(2048,0): at Microsoft.CodeAnalysis.CSharp.Binder.BindArgumentValue(DiagnosticBag diagnostics, ArgumentSyntax argumentSyntax, Boolean allowArglist, RefKind refKind)
...

        [Fact]
        public void DefaultInAsOperatorWithReferenceType()
        {
            var text = @"
class C
{
    static void Main()
    {
        System.Console.Write(default as C);
    }
}";

            var comp = CreateCompilationWithMscorlib(text, parseOptions: TestOptions.ExperimentalParseOptions, options: TestOptions.DebugExe);
            comp.VerifyDiagnostics(
             // TODO
                );
        }