[dynamo][guards-cpp-refactor] WEAKREF_ALIVE guard (#120344)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/120344
Approved by: https://github.com/jansel
ghstack dependencies: #119822, #119827, #119833, #120060, #120061, #120062, #120064, #120065, #120067, #120068, #120089, #120091, #120119, #120123, #120093, #120096, #120342
