get_value_set_rec: Replace mutable class member by additional parameter

There is no change in behaviour here, just cleanup to avoid a use of
`mutable` that was only put in place to keep the code churn to a
minimum.

Author: tautschnig

jbmc/unit/pointer-analysis/custom_value_set_analysis.cpp

@@ -78,6 +78,7 @@ class test_value_sett:public value_sett
   void get_value_set_rec(
     const exprt &expr,
     object_mapt &dest,
+    bool &includes_nondet_pointer,
     const std::string &suffix,
     const typet &original_type,
     const namespacet &ns) const override
@@ -91,7 +92,7 @@ class test_value_sett:public value_sett
     else
     {
       value_sett::get_value_set_rec(
-        expr, dest, suffix, original_type, ns);
+        expr, dest, includes_nondet_pointer, suffix, original_type, ns);
     }
   }