RFR(XS): 8011901: Unsafe.getAndAddLong(obj, off, delta) does not work properly with long deltas

[Roland Westrelin]

Hi Vladimir,

> The fix is correct, only movq instruction can load 64bit immediate value. I looked on other instructions (in x86_64.ad and x86.ad) with immL parameter and all of them use movq only. Could you double check?

Thanks for the review. I checked and I don't see immL being used with anything but movq either.

> Also remove unused "enc_class Con64" to avoid its usage by accident.

I will.

Roland.