Vendor deps.

vendor/syn/tests/macros/mod.rs

@@ -0,0 +1,7 @@
+macro_rules! errorf {
+    ($($tt:tt)*) => {{
+        use ::std::io::Write;
+        let stderr = ::std::io::stderr();
+        write!(stderr.lock(), $($tt)*).unwrap();
+    }};
+}