macOS: print stackoverflow warning if the overflow happened inside GC (…

…JuliaLang#55211)

See discussion in JuliaLang#55192.

I'm not sure how easy it is to recover from a stack overflow inside the
GC (or whether we should even try to do it), but we should at least
print a stack overflow warning here IMO.

src/signals-mach.c

@@ -294,10 +294,13 @@ static void segv_handler(int sig, siginfo_t *info, void *context)
  jl_task_t *ct = jl_get_current_task();
  jl_ptls_t ptls = ct == NULL ? NULL : ct->ptls;
  jl_call_in_state(ptls, (host_thread_state_t*)jl_to_bt_context(context), &jl_sig_throw);
+ return;
  }
- else {
- sigdie_handler(sig, info, context);
+ jl_task_t *ct = jl_get_current_task();
+ if ((sig != SIGBUS || info->si_code == BUS_ADRERR) && is_addr_on_stack(ct, info->si_addr)) { // stack overflow and not a BUS_ADRALN (alignment error)
+ stack_overflow_warning();
  }
+ sigdie_handler(sig, info, context);
 }
 
 // n.b. mach_exc_server expects us to define this symbol locally