Move-assign a posix::basic_stream_descriptor
from another.
basic_stream_descriptor & operator=( basic_stream_descriptor && other);
This assignment operator moves a stream descriptor from one object to another.
The other posix::basic_stream_descriptor
object from which the move will occur.
Following the move, the moved-from object is in the same state as if constructed
using the basic_stream_descriptor(io_service&) constructor
.