Buildings and grounds acquired under this chapter or prior to May 7, 1926, acquired or authorized for the use of the diplomatic and consular establishments in foreign countries may be used, in the case of buildings and grounds for the diplomatic establishment, as Government offices or residences or as such offices and residences; or, in the case of other buildings and grounds, as such offices or such offices and residences. The contracts for purchases of buildings, for leases, and for all work of construction, alteration, and repair under this chapter are authorized to be negotiated, the terms of the contracts to be prescribed, and the work to be performed, where necessary, without regard to such statutory provisions as relate to the negotiation, making, and performance of contracts and performance of work in the United States and without regard to section 3324(a) and (b) of title 31.