Don't use eax on x64. :)

src/x64/lithium-codegen-x64.cc

Index: src/x64/lithium-codegen-x64.cc
diff --git a/src/x64/lithium-codegen-x64.cc b/src/x64/lithium-codegen-x64.cc
index 12d912c396f1a146b1326628f20dbbd91d90681b..0bf218d864ff2872d368c865b8a30e2c4eecd329 100644
--- a/src/x64/lithium-codegen-x64.cc
+++ b/src/x64/lithium-codegen-x64.cc
@@ -1529,7 +1529,7 @@ void LCodeGen::CallKnownFunction(Handle<JSFunction> function,
     __ movq(rsi, FieldOperand(rdi, JSFunction::kContextOffset));
   }
 
-  // Set eax to arguments count if adaption is not needed. Assumes that eax
+  // Set rax to arguments count if adaption is not needed. Assumes that rax
   // is available to write to at this point.
   if (!function->NeedsArgumentsAdaption()) {
     __ Set(rax, arity);
@@ -1554,7 +1554,7 @@ void LCodeGen::CallKnownFunction(Handle<JSFunction> function,
 
 
 void LCodeGen::DoCallConstantFunction(LCallConstantFunction* instr) {
-  ASSERT(ToRegister(instr->result()).is(eax));
+  ASSERT(ToRegister(instr->result()).is(rax));
   __ Move(rdi, instr->function());
   CallKnownFunction(instr->function(), instr->arity(), instr);
 }