Fix bailing out of SSA compilation and enable --use-ssa on x64 by default.

vm/compiler.cc

Index: vm/compiler.cc
===================================================================
--- vm/compiler.cc	(revision 9284)
+++ vm/compiler.cc	(working copy)
@@ -268,6 +268,10 @@
                                      optimized,
                                      FLAG_use_ssa)) {
       // Compile again using non-ssa code generation.
+      // Re-parse because of side-effects to the AST during compilation.
+      ParsedFunction parsed_function(function);
+      Parser::ParseFunction(&parsed_function);
+      parsed_function.AllocateVariables();
       CompileParsedFunctionHelper(parsed_function, optimized, false);
     }