It was replaced by the GData lock and g_datalist_id_update_atomic().
Note that we introduced object_bit_lock() to replace global mutexes.
Now, object_bit_lock() is itself completely replaced, by the GData lock
(and hooking it via g_datalist_id_update_atomic()).
This means, all mutex-like locks now only go through the GData lock on
the GObject's qdata.
The object_bit_lock() API is still here, because it might be useful. For
example, there might be cases where the GData lock is not sufficient.
Also, we introduced GObjectPrivate mainly for object_bit_lock(). On 32
bit architecture, there is an overhead with that, as we cannot fit the
optional_flags into GObject. This is not dropped either. The optional
flags seem rather useful even without the object_bit_lock(). For
example, the OPTIONAL_FLAG_EVER_HAD_WEAK_REF flag is an important
optimization.
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