fix framework assembly resolution for net35 (#2557)

TestAssets/TestProjects/TestLibraryWithMultipleFrameworks/Program.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Xml;
 
 namespace ConsoleApplication
 {
@@ -7,6 +8,10 @@ namespace ConsoleApplication
         public static void Main()
         {
             Console.WriteLine("Hello World!");
+#if NET20 || NET35 || NET45 || NET461
+            // Force XmlDocument to be used
+            var doc = new XmlDocument();
+#endif
         }
     }
 }