refactor errno_from_ioerror

src/error.rs

@@ -1,5 +1,4 @@
 use crate::host;
-use crate::sys::errno_from_ioerror;
 use failure::Fail;
 use std::convert::Infallible;
 use std::fmt;
@@ -254,3 +253,13 @@ impl fmt::Display for Error {
         }
     }
 }
+
+fn errno_from_ioerror(e: &std::io::Error) -> host::__wasi_errno_t {
+    match e.raw_os_error() {
+        Some(code) => crate::sys::errno_from_host(code),
+        None => {
+            log::debug!("Inconvertible OS error: {}", e);
+            host::__WASI_EIO
+        }
+    }
+}