Unfortunately, I can't get it to work either. And I cannot find a workaround.
If you compile with --gen_func_subsections, all of the dead functions will be eliminated. You do lose out a bit in that all of the function calls are performed with the long call instruction, and not the short one. This feature of generating and then using a list of dead functions is intended to get the benefits of both dead function removal and short calls. For details see appendix A of this application note.
More unfortunate still is that the C5500 compiler is no longer under active development. Any problems, like this one, which are found are very unlikely to be addressed.
Thanks and regards,
-George