Include racy reads in Rust memory model with `MaybeInvalid<T>`

josh:

The kind of thing I'd like to be able to build in Rust, and can build today in C,

C and Rust use the same memory model (the one from C++) so I don't think there is anything you can build today in C that you can't build in Rust. I am curious why you think the "obvious" translation from C to Rust would not work.