C++11 deprecates implicit default copy constructors and operators if the class
has user-defined destructor or copy constructor/operator. gcc 9 generates
warnings when this deprecated language feature is used. This commit fixes that
by providing user-defained copy constructors/operators where needed. The
added definitions are equivalent to the implicitly generated by the compiler.
For thread::id, removed copy constructor to allow the compiler generate all
set of constructors and assignment operators, including move.
