fixup! src: do not use std::function for OnScopeLeave

src/util.h

@@ -503,7 +503,23 @@ template <typename T> inline void USE(T&&) {}
 template <typename Fn>
 struct OnScopeLeaveImpl {
   Fn fn_;
-  ~OnScopeLeaveImpl() { fn_(); }
+  bool active_;
+
+  explicit OnScopeLeaveImpl(Fn&& fn) : fn_(std::move(fn)), active_(true) {}
+  ~OnScopeLeaveImpl() { if (active_) fn_(); }
+
+  OnScopeLeaveImpl(const OnScopeLeaveImpl& other) = delete;
+  OnScopeLeaveImpl& operator=(const OnScopeLeaveImpl& other) = delete;
+  OnScopeLeaveImpl(OnScopeLeaveImpl&& other)
+    : fn_(std::move(other.fn_)), active_(other.active_) {
+    other.active_ = false;
+  }
+  OnScopeLeaveImpl& operator=(OnScopeLeaveImpl&& other) {
+    if (this == &other) return *this;
+    this->~OnScopeLeave();
+    new (this)OnScopeLeaveImpl(std::move(other));
+    return *this;
+  }
 };
 
 // Run a function when exiting the current scope. Used like this: