6647361: use Unsafe.put*Volatile methods to set final fields during default deserialization

[Clemens Eisserer]

> I've also been concerned about performance. As I understand it, but maybe
> I have
> it wrong, is that the JLS [1] doesn't allow this when changing final
> fields
> after an object is constructed.

But don't we have the same overhead at object construction time?
I remember having read somewhere the JVM issues fence/barrier
instructions after an object has been created?

- Clemens