[Bug middle-end/117871] cfg_hooks variables should be const at least and maybe a virtual functions

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117871

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
So this depends on removing sel scheduling.

Which does this mess:
```
void
sel_register_cfg_hooks (void)
{
  sched_split_block = sel_split_block;

  orig_cfg_hooks = get_cfg_hooks ();
  sel_cfg_hooks = orig_cfg_hooks;

  sel_cfg_hooks.create_basic_block = sel_create_basic_block;

  set_cfg_hooks (sel_cfg_hooks);
```