Support g_auto* macros
g_autofree, ptr and so on are such nice features against developers manually free resources or cause memory leaks by accident.
Note that we could migrate current implementation to G_DECLARE_/G_DEFINE_ macros, but in that case, the ABI could be broken. This should be discussed.
For workaround, just use
G_DEFINE_AUTOPTR_CLEANUP_FUNC in header files.