Cannot build Xamarin.IOS project with 1.0.0-rc

After I update to 1.0.0-rc, I got the following error message at build time:

```
/path/to/MTOUCH: Error MT2002: Failed to resolve
"System.CodeDom.CodeParameterDeclarationExpression" reference from
"System.CodeDom, Version=4.0.0.0, Culture=neutral,
PublicKeyToken=cc7b13ffcd2ddd51" (MT2002)
```