Julia segfaults when killed

[Keno]

It's trying to set up an exception frame, but the signal thread is not associated with a task:

1|debug > bt
[1] jl_enter_handler  at /home/kfischer/julia/src/builtins.c:200
[2] jl_atexit_hook  at /home/kfischer/julia/src/init.c:233
[3] jl_exit  at /home/kfischer/julia/src/jl_uv.c:537
[4] signal_listener  at ./signals-unix.c:458
[5] start_thread  at pthread_create.c:312

1|debug > f 1
Stopped in function jl_enter_handler
In builtins.c:195
199       // Must have no safepoint
200       eh->prev = current_task->eh;
201       eh->gcstack = ptls->pgcstack;
202   #ifdef JULIA_ENABLE_THREADING

1|C++ > current_task
(jl_task_t *) 0x0

[yuyichao]

Dup of #17706