function lazyJoinStacks (targetError, sourceError) {
var targetStack = Object.getOwnPropertyDescriptor(targetError, 'stack');

Object.defineProperty(targetError, 'stack', {
  get: function () {
    return joinStacks(targetStack.get.apply(targetError), sourceError.stack);
  },
  enumerable: false,
  configurable: true
});
}
Calls {@link joinStacks} lazily, when the {@link Error#stack} property is accessed.

@param {Error} targetError
@param {Error} sourceError