use virtual destructors

Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>

src/sat/ba/ba_internalize.h

@@ -46,6 +46,7 @@ namespace sat {
         literal internalize_xor(expr* e, bool sign, bool root);
     public:
         ba_internalize(ba_solver& ba, solver_core& s, ast_manager& m) : m(m), pb(m), ba(ba), m_solver(s) {}
+        ~ba_internalize() override {}
         literal internalize(sat_internalizer& si, expr* e, bool sign, bool root) override;
         
     };

src/sat/euf/euf_solver.h

@@ -93,6 +93,7 @@ namespace euf {
             m_eq_idx(this, 1),
             m_lit_idx(this, 2)
         {}
+        ~solver() override {}
 
         void set_solver(sat::solver* s) override { m_solver = s; }
         void set_lookahead(sat::lookahead* s) override { m_lookahead = s; }

src/sat/smt/sat_smt.h

@@ -49,6 +49,7 @@ namespace sat {
     class th_internalizer {
     public:
         virtual literal internalize(sat_internalizer& si, expr* e, bool sign, bool root) = 0;
+        virtual ~th_internalizer() {}
     };
 
     class index_base {