fix macos empty metadata test

Author: pvdrz

tests/run-pass/fs.rs

@@ -18,7 +18,9 @@ fn test_metadata(bytes: &[u8], path: &Path) -> Result<()> {
 
 // FIXME: Implement stat64 for macos.
 #[cfg(not(target_os = "linux"))]
-fn test_metadata(_bytes: &[u8], _path: &Path) {}
+fn test_metadata(_bytes: &[u8], _path: &Path) -> Result<()> {
+    Ok(())
+}
 
 fn main() {
     let tmp = std::env::temp_dir();