[perl #87708] use integer; $tied == $tied

[perl #87708] use integer; $tied == $tied

This is just part of #87708.

This fixes == under ‘use integer’ when the same tied scalar is used
for both operands and returns two different values. Before this com-
mit, get-magic would be called only once and the same value used. In
5.12.x it just worked.