[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/wasi.rs

@@ -95,7 +95,7 @@ impl AsBytes for types::Dirent {
         let mut bytes: Vec<u8> = Vec::with_capacity(offset);
         bytes.resize(offset, 0);
         let ptr = bytes.as_mut_ptr() as *mut Self;
-        unsafe { ptr.write_unaligned(*self) };
+        unsafe { ptr.write_unaligned(self.clone()) };
         Ok(bytes)
     }
 }