Compatibility fixes with thread-safe list tracker changes.

src/utils/functional.h

@@ -0,0 +1,21 @@
+#ifndef RTORRENT_UTILS_FUNCTIONAL_H
+#define RTORRENT_UTILS_FUNCTIONAL_H
+
+#include <functional>
+
+namespace utils {
+
+// Create a class that calls a std::function when returning or exiting a scope.
+class scope_guard {
+public:
+  scope_guard(std::function<void()> on_exit_scope) : m_on_exit_scope(on_exit_scope) {}
+  ~scope_guard() { m_on_exit_scope(); }
+
+private:
+  std::function<void()> m_on_exit_scope;
+};
+
+} // namespace utils
+
+#endif
+