The gold that the IMF would be selling is for itself, those sales would have no material impact on any of the major nations. If my memory is correct, they were short strapped for cash to lend to Argentina, Brazil and the like a few years ago. Americans were reluctant to lend money without strings attached. So the IMF had to find creative means of finding cash to lend them and I suspect the scenario has not improved.
Those are IMF affairs but Americans do have a major say in the goings on for historically I believe they were major lenders and financial supporters of IMF opperations, much like the UN.

As most state, this possible sale is just rhetoric for psycholigical effect.
It is a sign of desperation. JMO.