syntax: Remove io_error usage

src/libsyntax/lib.rs

@@ -33,6 +33,11 @@ This API is completely unstable and subject to change.
 extern mod extra;
 extern mod term;
 
+#[cfg(stage0)]
+macro_rules! if_ok (
+    ($e:expr) => (match $e { Ok(e) => e, Err(e) => return Err(e) })
+)
+
 pub mod util {
     pub mod interner;
     #[cfg(test)]