Link test/regress with event_core/event_extra over event Due to regress linked with event and event_core (both of them includes evthread.c) there will be two different evthread_id_fn_ variables under mingw64: evthread_id_fn_: &0x5294f20a8 evthread_id_fn_: &0x4ba0030a8 And because of this evthread_use_pthreads() can/will set one copy of variables while evthread*() functions will access another, which will break a lot of things (for example main/del_notify test). Fixes: #792