Fix building with PCH disabled.

Source/Core/Core/FifoPlayer/FifoPlayer.cpp

@@ -3,6 +3,7 @@
 // Refer to the license.txt file included.
 
 #include <algorithm>
+#include <mutex>
 
 #include "Common/CommonTypes.h"
 #include "Core/ConfigManager.h"

Source/Core/Core/FifoPlayer/FifoRecorder.cpp

@@ -3,6 +3,7 @@
 // Refer to the license.txt file included.
 
 #include <algorithm>
+#include <mutex>
 
 #include "Common/Thread.h"
 #include "Core/ConfigManager.h"