[wiggle] Don't make generated structs and unions Copy.

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.

crates/wasi-common/src/clock.rs

@@ -5,7 +5,7 @@ use std::time::SystemTime;
 
 pub(crate) use sys::clock::*;
 
-pub(crate) fn to_relative_ns_delay(clock: SubscriptionClock) -> Result<u128> {
+pub(crate) fn to_relative_ns_delay(clock: &SubscriptionClock) -> Result<u128> {
     if clock.flags != Subclockflags::SUBSCRIPTION_CLOCK_ABSTIME {
         return Ok(u128::from(clock.timeout));
     }