wasi-common: trace and convert error

this is a bug - the TODO was never resolved, even when the code to
implement it was added right below :)

tracing is already in the transitive deps via wiggle, so no extra
trouble there. tracing::debug is more appropriate than eprintln

crates/wasi-common/Cargo.toml

@@ -27,6 +27,7 @@ filetime = "0.2.7"
 lazy_static = "1.4.0"
 wig = { path = "wig", version = "0.19.0" }
 wiggle = { path = "../wiggle", default-features = false, version = "0.19.0" }
+tracing = "0.1.19"
 
 [target.'cfg(unix)'.dependencies]
 yanix = { path = "yanix", version = "0.19.0" }