C++: add GVN import to fix reevaluation

Author: rdmarsh2

cpp/ql/src/Security/CWE/CWE-078/ExecTainted.ql

@@ -16,9 +16,10 @@
 import cpp
 import semmle.code.cpp.security.CommandExecution
 import semmle.code.cpp.security.Security
+import semmle.code.cpp.valuenumbering.GlobalValueNumbering
+import semmle.code.cpp.ir.IR
 import semmle.code.cpp.ir.dataflow.TaintTracking
 import semmle.code.cpp.ir.dataflow.TaintTracking2
-import semmle.code.cpp.ir.IR
 import semmle.code.cpp.security.FlowSources
 import semmle.code.cpp.models.implementations.Strcat