LibC: Implement tfind and tsearch

Userland/Libraries/LibC/bits/search.h

@@ -0,0 +1,18 @@
+/*
+ * Copyright (c) 2021, the SerenityOS developers.
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+// This is technically an implementation detail, but we require this for testing.
+// The key always has to be the first struct member.
+struct search_tree_node {
+    const void* key;
+    struct search_tree_node* left;
+    struct search_tree_node* right;
+};
+
+struct search_tree_node* new_tree_node(const void* key);
+void delete_node_recursive(struct search_tree_node* node);