Update to Wasmtime 38.0.4 and wasm-tools 240 (#3359)

No major changes here, just a routine update. This notably does not
update to today's release of Wasmtime 39.0.0 since I some changes in
Wasmtime are necessary, but that'll get fixed by 40.0.0

Signed-off-by: Alex Crichton <[email protected]>

Author: alexcrichton