As motivated in D60598, this drops support for specifying both NUW and NSW in makeGuaranteedNoWrapRegion(). None of the users of this function currently make use of this.
When both NUW and NSW are specified, the exact nowrap region has two disjointed parts and makeGNWR() returns one of them. This result doesn't seem to be useful for anything, but makes the semantics of the function fuzzier.
After this change, I'd land an NFC rename from makeGuaranteedNoWrapRegion() to makeExactNoWrapRegion().