CXXD_MEM_FN_HEADER — The mem_fn header file name.
// In header: <boost/cxx_dual/impl/mem_fn.hpp> CXXD_MEM_FN_HEADER
The object-like macro expands to the include header file designation for the mem_fn header file. The macro is used with the syntax: #include CXXD_MEM_FN_HEADER
