fix the multi tfm test to not build net20

TestAssets/TestProjects/TestLibraryWithTwoFrameworks/Program.cs

@@ -0,0 +1,17 @@
+using System;
+using System.Xml;
+
+namespace ConsoleApplication
+{
+    public class Program
+    {
+        public static void Main()
+        {
+            Console.WriteLine("Hello World!");
+#if NET20 || NET35 || NET45 || NET461
+            // Force XmlDocument to be used
+            var doc = new XmlDocument();
+#endif
+        }
+    }
+}

TestAssets/TestProjects/TestLibraryWithTwoFrameworks/project.json

@@ -0,0 +1,20 @@
+{
+  "version": "1.0.0-*",
+  "buildOptions": {
+    "emitEntryPoint": false
+  },
+  "dependencies": {},
+  "frameworks": {
+    "net461": {
+      "frameworkAssemblies": {
+        "System.Xml": {}
+      }
+    },
+    "netstandard1.5": {
+      "imports": "dnxcore50",
+      "dependencies": {
+        "NETStandard.Library": "1.6.0"
+      }
+    }
+  }
+}