why thread functions need announced '__cdecl'?

sample formula shows emanate threads controlling mfc declares thread duty both stationary __cdecl. since latter required? boost threads don't worry convention, only an anachronism?

for instance (mfc):

static __cdecl uint myfunc(lpvoid pparam)
{
...
}

cwinthread* pthread = afxbeginthread(myfunc, ...);

whereas boost:

static vacant func()
{
...
}

boost::thread t;
t.create(&func);

(the formula samples competence 100% repremand i am nowhere circuitously an ide).

what indicate __cdecl? does assistance formulating threads?