Enable crossgen for CLI SDK binaries.

TODO: Write tests to make sure aseemblies are crossgened.

scripts/dotnet-cli-build/Utils/PEUtils.cs

@@ -0,0 +1,27 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Reflection.PortableExecutable;
+
+namespace Microsoft.DotNet.Cli.Build
+{
+    public class PEUtils
+    {
+        public static bool HasMetadata(string pathToFile)
+        {
+            try
+            {
+                using (var inStream = File.OpenRead(pathToFile))
+                {
+                    using (var peReader = new PEReader(inStream))
+                    {
+                        return peReader.HasMetadata;
+                    }
+                }
+            }
+            catch (BadImageFormatException) { }
+
+            return false;
+        }
+    }
+}