cpp/io/basic osyncstream/basic osyncstream

Constructs new synchronized output stream

@1-4@ constructs the private member using the buffer and the allocator provided, and initializes the base class with a pointer to the member. @5@ Move constructor. Move-constructs the base and the std::basic_syncbuf member from the corresponding subobjects of, then calls  with the pointer to the newly-constructed underlying  to complete the initialization of the base. After this move constructor, returns  and destruction of  produces no output.