ioctl_tree: Quiesce analyzer false positive

It claims that

```
src/ioctl_tree.c:305:17: error: check of ‘node’ for NULL after already dereferencing it [-Werror=analyzer-deref-before-chec
k]
  305 |     for (; node != NULL; node = node->parent)
      |                 ^
  ‘ioctl_tree_next’: events 1-4
    |
    |  300 |     if (node->child != NULL)
    |      |        ~~~~~^~~~~~~
    |      |        |    |
    |      |        |    (1) pointer ‘node’ is dereferenced here
    |      |        (2) following ‘false’ branch...
    |  301 |         return node->child;
    |  302 |     if (node->next != NULL)
    |      |        ~~~~~~~~~~~
    |      |        |    |
    |      |        |    (3) ...to here
    |      |        (4) following ‘false’ branch...
    |
  ‘ioctl_tree_next’: event 5
    |
    |cc1:
    | (5): ...to here
    |
  ‘ioctl_tree_next’: event 6
    |
    |  305 |     for (; node != NULL; node = node->parent)
    |      |                 ^
    |      |                 |
    |      |                 (6) pointer ‘node’ is checked for NULL here but it was already dereferenced at (1)
```

But this is bogus -- the for loop first moves node to node->parent and
then checks against NULL. The same happens when rewriting it as a while
loop.

src/ioctl_tree.c

@@ -301,10 +301,17 @@ ioctl_tree_next(const ioctl_tree * node)
 	return node->child;
     if (node->next != NULL)
 	return node->next;
+
+    /* HACK: -fanalyzer does not understand this loop */
+#pragma GCC diagnostic push
+#if !defined(__clang__)
+#pragma GCC diagnostic ignored "-Wanalyzer-deref-before-check"
+#endif
     /* walk up the parents until we find an alternative sibling */
     for (; node != NULL; node = node->parent)
 	if (node->next != NULL)
 	    return node->next;
+#pragma GCC diagnostic pop
 
     /* no alternative siblings left, iteration done */
     return NULL;