[util.smartptr.shared.create] before p2 shows a broken make_shared and allocate_shared prototype declaration presumably due to an incomplete \placeholder{} expansion. In addition, the variadic template parameter name Args is missing (I just checked p0674r1 and found that the omitted parameter seemed to be intended):

template<class T, ...>
shared_ptr<T> make_shared(\placeholder{args});
template<class T, class A, ...>
shared_ptr<T> allocate_shared(const A& a, \placeholder{args});