90ff6fcd4e
PR #94586 added support for using `rustc_nonnull_optimization_guaranteed` on values where the "null" value is the all-ones bitpattern. Now that #94586 has made it to the stage0 compiler, add `rustc_nonnull_optimization_guaranteed` to `OwnedFd`, `BorrowedFd`, `OwnedSocket`, and `BorrowedSocket`, since these types all exclude all-ones bitpatterns. This allows `Option<OwnedFd>`, `Option<BorrowedFd>`, `Option<OwnedSocket>`, and `Option<BorrowedSocket>` to be used in FFI declarations, as described in the [I/O safety RFC]. [I/O safety RFC]: https://github.com/rust-lang/rfcs/blob/master/text/3128-io-safety.md#ownedfd-and-borrowedfdfd-1