LibC: Fix stack_t::ss_sp type from void** -> void*

userspace/libraries/LibC/include/signal.h

@@ -141,7 +141,7 @@ struct sigevent
 
 typedef struct
 {
-	void** ss_sp;    /* Stack base or pointer. */
+	void*  ss_sp;    /* Stack base or pointer. */
 	size_t ss_size;  /* Stack size. */
 	int    ss_flags; /* Flags. */
 } stack_t;