Add code for CPU feature detection and use it to detect SSE3 and SSE 4.1.

runtime/bin/gen_snapshot.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // Generate a snapshot file after loading all the scripts specified on the
 // command line.
 
 #include <stdlib.h>
 #include <string.h>
 #include <stdio.h>
@@ skipping 281 matching lines @@
     return 255;
   }
 
   DartUtils::SetOriginalWorkingDirectory();
 
   Dart_SetVMFlags(vm_options.count(), vm_options.arguments());
 
   // Initialize the Dart VM.
   // Note: We don't expect isolates to be created from dart code during
   // snapshot generation.
-  Dart_Initialize(NULL, NULL, NULL);
+  if (!Dart_Initialize(NULL, NULL, NULL)) {
+    fprintf(stderr, "VM initialization failed\n");
+    return 255;
+  }
 
   char* error;
   Dart_Isolate isolate = Dart_CreateIsolate(NULL, NULL, NULL, NULL, &error);
   if (isolate == NULL) {
     fprintf(stderr, "Error: %s", error);
     free(error);
     exit(255);
   }
 
   Dart_Handle result;
@@ skipping 68 matching lines @@
 
       // Now create and write snapshot of script.
       CreateAndWriteSnapshot(true);
     }
   } else {
     SetupForGenericSnapshotCreation();
     CreateAndWriteSnapshot(false);
   }
   return 0;
 }