Count trace_running for internal event
I want to fix a crash: https://gist.github.com/k0kubun/86fd9fbff32423bd4974
I noticed that clean_hooks can be executed inside exec_hooks_body.
The hooks of list->hooks can be xfreed during exec_hooks_body.
That's because th->vm->trace_running is not incremented for exec_hooks_unprotected.
So I fixed rb_threadptr_exec_event_hooks_orig to count exec_hooks_unprotected as th->vm->trace_running too.