C/C++ overlay: Update identical files

Author: IdrissRio

config/identical-files.json

@@ -282,6 +282,7 @@
     "java/ql/lib/semmle/code/java/internal/OverlayXml.qll",
     "go/ql/lib/semmle/go/internal/OverlayXml.qll",
     "python/ql/lib/semmle/python/internal/OverlayXml.qll",
-    "csharp/ql/lib/semmle/code/csharp/internal/OverlayXml.qll"
+    "csharp/ql/lib/semmle/code/csharp/internal/OverlayXml.qll",
+    "cpp/ql/lib/semmle/code/cpp/internal/OverlayXml.qll"
   ]
 }