C++: Restrict 'VariableNode's to only be global-like variables (which is the only place where use them for).

Author: MathiasVP

cpp/ql/lib/semmle/code/cpp/ir/dataflow/internal/DataFlowUtil.qll

@@ -34,7 +34,7 @@ private import Node0ToString
 cached
 private newtype TIRDataFlowNode =
   TNode0(Node0Impl node) { DataFlowImplCommon::forceCachingInSameStage() } or
-  TVariableNode(Variable var, int indirectionIndex) {
+  TVariableNode(GlobalLikeVariable var, int indirectionIndex) {
     indirectionIndex =
       [getMinIndirectionsForType(var.getUnspecifiedType()) .. Ssa::getMaxIndirectionsForType(var.getUnspecifiedType())]
   } or