forked from boostorg/smart_ptr
Saves up to sizeof(void*) + sizeof(size_t) bytes for make_shared and saves sizeof(void*) + sizeof(size_t) + sizeof(A) bytes for allocate_shared where A is the supplied allocator type.
Saves up to sizeof(void*) + sizeof(size_t) bytes for make_shared and saves sizeof(void*) + sizeof(size_t) + sizeof(A) bytes for allocate_shared where A is the supplied allocator type.