Some structs and unions are large enough that making them `Copy` isn't ideal. wasi-common only needed `Copy` in a few places that were easy to fix. `SubscriptionClock` is 32 bytes, so it's not a bad a idea to pass it by reference anyway.
wiggle
Wiggle is a code generator for the host side of a witx interface. It is
invoked as a Rust procedural macro.
Wiggle is not specialized to any particular WebAssembly runtime. It is usable in at least Wasmtime and Lucet.