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

runtime/bin/gen_snapshot.cc

Index: runtime/bin/gen_snapshot.cc
===================================================================
--- runtime/bin/gen_snapshot.cc	(revision 12828)
+++ runtime/bin/gen_snapshot.cc	(working copy)
@@ -299,7 +299,10 @@
   // 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;

[srdjan, 2012/09/25 17:12:25]

Why not exit(255) as below?

[Florian Schneider, 2012/09/26 09:03:16]

Because I copied it from above where return 255 is used :)
return seems cleaner to me since it also invokes destructors of stack-allocated
objects (e.g. CommandLineOptions)

I don't think that it matters here. exit() is used in many functions in case of
an error, so it would mean changing a lot to get rid of it.

+  }
 
   char* error;
   Dart_Isolate isolate = Dart_CreateIsolate(NULL, NULL, NULL, NULL, &error);