Returns the value 1 (TRUE) if either or both of the arguments is
    a NaN. Otherwise, it returns the value 0 (FALSE).

    This function is supported on OpenVMS Integrity servers and
    Alpha only.

    Format

      #include  <math.h>

      double unordered  (double x, double y);

      float unorderedf  (float x, float y);

      long double unorderedl  (long double x, long double y);