hb_object's user_data is created lazily. The previous implementation of
hb_object_set_user_data created space for the user_data but did not
actually construct it. This means that hb_user_data_array_t's lock was
not constructed. If hb_mutex_t is backed by an implementation which
requires that it be constructed (not just zero initialized) then errors
will occur when taking the lock when setting the user data.
Change hb_object_set_user_data to construct the user_data in the created
space and hb_object_fini to call the destructor.
Was good idea, but with C++ types with constructor/destructor, was getting in
the way as compiler was destructing those items where it was not desired.
Since C++ does not allow zero-sized arrays, just remove it...
Newer compilers / language allows structs with constructor in union.
So, this was not actually testing anything. Indeed, the recent
change in DISALLOW_COPY *is* making some of our types non-POD.
That broke some bots.
Just remove this since it wasn't doing much, and I'd rather have
DISALLOW_COPY.