GCC 12 complains if a reference to an uninitialized object is
being passed to a constructor. The mysql_mutex_t, mysql_cond_t
would be initialized in the constructor body, which is executed
after the initializer list. There is no problem passing a pointer
instead of a reference. The wrapper classes do not dereference
the pointers in the constructor or destructor, so there does not
appear to be any correctness issue.