Locked<T>: optimistically use SpinMutex to consume less RAM

std::mutex is 5 pointers large on x64, whereas std::atomic_flag at most one.

lib/base/atomic.hpp

@@ -84,20 +84,20 @@ class Locked
 public:
 	inline T load() const
 	{
-		std::unique_lock<std::mutex> lock(m_Mutex);
+		std::unique_lock lock (m_Mutex);
 
 		return m_Value;
 	}
 
 	inline void store(T desired)
 	{
-		std::unique_lock<std::mutex> lock(m_Mutex);
+		std::unique_lock lock (m_Mutex);
 
 		m_Value = std::move(desired);
 	}
 
 private:
-	mutable std::mutex m_Mutex;
+	mutable SpinMutex m_Mutex;
 	T m_Value;
 };