fixes

src/error.rs

@@ -3,6 +3,7 @@ use crate::sys::errno_from_ioerror;
 use failure::Fail;
 use std::fmt;
 use std::num::TryFromIntError;
+use std::convert::Infallible;
 
 #[derive(Clone, Copy, Debug, Fail)]
 pub enum WasiError {
@@ -134,6 +135,12 @@ impl From<TryFromIntError> for Error {
     }
 }
 
+impl From<Infallible> for Error {
+    fn from(_: Infallible) -> Self {
+        unreachable!()
+    }
+}
+
 #[cfg(windows)]
 impl From<winx::winerror::WinError> for Error {
     fn from(err: winx::winerror::WinError) -> Self {