[clang] [Clang][C++23] Implement P1774R8: Portable assumptions (PR #81014)

[via cfe-commits]

Sirraide wrote:

> Of the three, I lean towards 3 actually, I think that is perhaps the BEST idea, and is perhaps supported by our existing infrastructure already (if you have Attr.td set its targets right?). I'd like to see what Aaron has to say, but I THINK that is my preference baring any concerns.

Yeah, I agree that that is probably the best option (though we should probably still update the diagnostic I mentioned, because it’s not obvious imo that `[[assume]]` != `[[clang::assume]]`).



https://github.com/llvm/llvm-project/pull/81014