PR fortran/23815: Add byte-swapping to gfortran

[Richard Henderson]

> So there should be support for kind=10.

I'm thinking of

      /* Only let float/double/long double go through because the fortran
         library assumes these are the only floating point types.  */

      if (mode != TYPE_MODE (float_type_node)
          && (mode != TYPE_MODE (double_type_node))
          && (mode != TYPE_MODE (long_double_type_node)))
        continue;

I'm not 100% in favour of this, but since I'm not willing to do the
library work to handle odd-sized types, for platforms I don't have
too much interest in, I accept it.


r~