ohcount doesn't build with recent versions of swig/ruby

[sylvestre]

> ruby/ohcount_wrap.c:2241:34: error: passing argument 3 of ‘rb_iterate’ from incompatible pointer type [-Wincompatible-pointer-types]
>  2241 |         rb_iterate(rb_each, val, SourceFileListItem_rb_add_directory, (VALUE)list);
>       |                                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>       |                                  |
>       |                                  VALUE (*)(VALUE,  SourceFileList *) {aka long unsigned int (*)(long unsigned int,  struct SourceFileListItem *)}

see https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1079834