Add missing functional include caused by PR111

Source/Core/Core/Debugger/Debugger_SymbolMap.cpp

@@ -2,6 +2,8 @@
 // Licensed under GPLv2
 // Refer to the license.txt file included.
 
+#include <functional>
+
 #include "Common/Common.h"
 #include "Common/StringUtil.h"