Add some debugging printfs when malloc fails and we don't have an

explicit call to sudo_warnx().

src/hooks.c

@@ -131,8 +131,11 @@ register_hook_internal(struct sudo_hook_list *head,
     struct sudo_hook_entry *hook;
     debug_decl(register_hook_internal, SUDO_DEBUG_HOOKS)
 
-    if ((hook = calloc(1, sizeof(*hook))) == NULL)
+    if ((hook = calloc(1, sizeof(*hook))) == NULL) {
+	sudo_debug_printf(SUDO_DEBUG_ERROR|SUDO_DEBUG_LINENO,
+	    "unable to allocate memory");
 	debug_return_int(-1);
+    }
     hook->u.generic_fn = hook_fn;
     hook->closure = closure;
     SLIST_INSERT_HEAD(head, hook, entries);