The right of election of a surviving spouse may be waived before or after marriage by a written contract, agreement, or waiver signed by the party waiving the right of election. Unless it provides to the contrary, a waiver of "all rights" in the property or estate of a present or prospective spouse, or a complete property settlement entered into after or in anticipation of separation or divorce, is a waiver of any right to his family allowance as well as to his elective share by each spouse in the property of the spouse, his right to letters under § 5-104, and is an irrevocable renunciation of any benefit which would pass to him from the other by intestate succession, by statutory share, or by virtue of the provisions of a will executed before the waiver or property settlement.