C++: Define an extractor version table and use in IR generation

cpp/ql/lib/semmlecode.cpp.dbscheme

@@ -197,6 +197,11 @@ svnchurn(
  * C++ dbscheme
  */
 
+extractor_version(
+    string codeql_version: string ref,
+    string frontend_version: string ref
+)
+
 @location = @location_stmt | @location_expr | @location_default ;
 
 /**