[Pre-RFC] usize is not size_t

[InfernoDeity]

@tcsc

It's very clear that in the past Rust has deliberately made the decision not to support certain exotic platforms in order to make the common case easier to program against, and I think that was a very good move

To be fair, w65 is less "exotic" than some. It has 8-bit bytes, and (mostly) well-behaved pointers in the ABI defined above (notably an abi-level change made to accomodate rust: see this zulip discussion (archive)). The main issue is the instant one - whether size_t can differ from uintptr_t.