wiggle::async_trait is defined as async_trait::async_trait(?Send)

async methods used by wiggle currently need to Not have the Send
constraint, so rather than make all use sites pass the argument
to the re-exported async_trait macro, define a new macro that
applies the argument.

crates/wiggle/src/lib.rs

@@ -6,9 +6,8 @@ use std::slice;
 use std::str;
 use std::sync::Arc;
 
-pub use wiggle_macro::from_witx;
-// re-exports so users of wiggle don't need to track the dependency:
-pub use async_trait::async_trait;
+pub use wiggle_macro::{async_trait, from_witx};
+
 pub use bitflags;
 
 #[cfg(feature = "wiggle_metadata")]
@@ -24,6 +23,10 @@ pub use error::GuestError;
 pub use guest_type::{GuestErrorType, GuestType, GuestTypeTransparent};
 pub use region::Region;
 
+pub mod async_trait_crate {
+    pub use async_trait::*;
+}
+
 /// A trait which abstracts how to get at the region of host memory taht
 /// contains guest memory.
 ///