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

Cargo.lock

@@ -2156,9 +2156,9 @@ dependencies = [
 
 [[package]]
 name = "tracing"
-version = "0.1.16"
+version = "0.1.19"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "c2e2a2de6b0d5cbb13fc21193a2296888eaab62b6044479aafb3c54c01c29fcd"
+checksum = "6d79ca061b032d6ce30c660fded31189ca0b9922bf483cd70759f13a2d86786c"
 dependencies = [
  "cfg-if",
  "log",
@@ -2168,9 +2168,9 @@ dependencies = [
 
 [[package]]
 name = "tracing-attributes"
-version = "0.1.9"
+version = "0.1.10"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f0693bf8d6f2bf22c690fc61a9d21ac69efdbb894a17ed596b9af0f01e64b84b"
+checksum = "1fe233f4227389ab7df5b32649239da7ebe0b281824b4e84b342d04d3fd8c25e"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -2179,9 +2179,9 @@ dependencies = [
 
 [[package]]
 name = "tracing-core"
-version = "0.1.11"
+version = "0.1.14"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "94ae75f0d28ae10786f3b1895c55fe72e79928fd5ccdebb5438c75e93fec178f"
+checksum = "db63662723c316b43ca36d833707cc93dff82a02ba3d7e354f342682cc8b3545"
 dependencies = [
  "lazy_static",
 ]
@@ -2326,6 +2326,7 @@ dependencies = [
  "libc",
  "log",
  "thiserror",
+ "tracing",
  "wig",
  "wiggle",
  "winapi",