Undefined symbols:
  "_z_dsp_setup", referenced from:
      _myfilter_new in simplelowpass.o
  "_dsp_add", referenced from:
      _myfilter_dsp in simplelowpass.o
  "_class_dspinit", referenced from:
      _main in simplelowpass.o
  "_z_dsp_free", referenced from:
      _z_dsp_free$non_lazy_ptr in simplelowpass.o
     (maybe you meant: _z_dsp_free$non_lazy_ptr)
ld: symbol(s) not found
collect2: ld returned 1 exit status