gio: Add missing assert_initialized_main_thread! macro definition

Author: sdroege

gio/src/lib.rs

@@ -6,6 +6,10 @@
 #![allow(clippy::missing_safety_doc)]
 #![doc = include_str!("../README.md")]
 
+macro_rules! assert_initialized_main_thread {
+    () => {};
+}
+
 pub use gio_sys as ffi;
 pub use glib;