…-variations.enabled.

Atomic<bool> is implemented in terms of AtomicBase<uint32_t>, because that way
you don't need to depend on atomic 1-byte operations.  That means that the rust
bindgen sees it as a u32, not a bool.

It's a bit concerning that the rust code seems to be doing an unsynchronized
read here, but given this is a RelaxedAtomic, that's probably ok.

Bug: 1467134
Reviewed-by: emilio