C++: Add a test that needs indirect barrier guards.

Author: MathiasVP

cpp/ql/test/library-tests/dataflow/dataflow-tests/BarrierGuard.cpp

@@ -1,5 +1,5 @@
 int source();
-void sink(int);
+void sink(...);
 bool guarded(int);
 
 void bg_basic(int source) {
@@ -66,3 +66,13 @@ void bg_structptr(XY *p1, XY *p2) { // $ ast-def=p1 ast-def=p2
     sink(p1->x); // $ ast,ir
   }
 }
+
+int* indirect_source();
+bool guarded(const int*);
+
+void bg_indirect_expr() {
+  int *buf = indirect_source();
+  if (guarded(buf)) {
+    sink(buf); // $ SPURIOUS: ir
+  }
+}