fix -Wunused-but-set-variable for gcc-4.6 on x64

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index 26ab64552fc344fff7be569d3f43b365650c4d6f..419ecacd1b9c795a0fb627149fb3f034c73cc545 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -2220,8 +2220,7 @@ MUST_USE_RESULT MaybeObject* JSProxy::SetPropertyWithHandler(
       receiver.location(), name.location(), value.location()
   };
   bool has_exception;
-  Handle<Object> result =
-      Execution::Call(trap, handler, ARRAY_SIZE(args), args, &has_exception);
+  Execution::Call(trap, handler, ARRAY_SIZE(args), args, &has_exception);
   if (has_exception) return Failure::Exception();
 
   return *value;