Avoid a hang after C-g while sit-for on a Unix TTY

* src/thread.c (acquire_global_lock): Don't try to take the global
lock if the same thread is already holding it.  (Bug#29347)

src/thread.c

@@ -97,6 +97,11 @@ post_acquire_global_lock (struct thread_state *self)
 static void
 acquire_global_lock (struct thread_state *self)
 {
+  /* If some Lisp was interrupted by C-g while inside pselect, the
+     signal handler could have called maybe_reacquire_global_lock, in
+     which case we are already holding the lock and shouldn't try
+     taking it again, or else we will hang forever.  */
+  if (!(self && self->not_holding_lock))
     sys_mutex_lock (&global_lock);
   post_acquire_global_lock (self);
 }