The right of election of a surviving spouse may be waived, wholly or partially, before or after marriage, by a written contract, agreement or waiver signed by the party waiving. Unless it provides to the contrary, a waiver of “all rights” (or equivalent language) 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 all rights to the elective share by each spouse in the property of the other and a renunciation by each of all benefits which would otherwise pass to each from the other by intestate succession or by virtue of any will executed before the waiver or property settlement.