Fix gen-windows-sys-binding (#1518)

Unwrap on warnings returned

Author: NobodyXu

dev-tools/gen-windows-sys-binding/src/main.rs

@@ -36,7 +36,8 @@ fn main() {
         "--filter",
         "--etc",
         &filter,
-    ]);
+    ])
+    .unwrap();
 
     let bindings =
         fs::read_to_string(temp_file.path()).expect("failed to read temp windows_sys.rs");