Wrapper for volatile fields

[tgross35]

In C, fields can be defined as volatile whereas for Rust it is the accesses. I'm wondering if we should consider wrapping any volatile members in some UnsafeCell-based wrapper to ensure they aren't read by accident.

Unfortunately this is a bit tricky since we can't allow it to be moved by the compiler.

[tgross35]

I'm thinking maybe we should provide a struct Volatile<T>(UnsafeCell<T>); wrapper type that at least makes it clear what these fields are, even if we can't actually enforce volatility.