address other warnings per input from delcypher

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

src/ast/rewriter/rewriter.h

@@ -111,7 +111,7 @@ protected:
     void elim_reflex_prs(unsigned spos);
 public:
     rewriter_core(ast_manager & m, bool proof_gen);
-    ~rewriter_core();
+    virtual ~rewriter_core();
     ast_manager & m() const { return m_manager; }
     void reset();
     void cleanup();

src/cmd_context/parametric_cmd.h

@@ -72,6 +72,7 @@ public:
         // m_params.set_func_decl(m_last, f); 
         // m_last = symbol::null; 
     }
+    virtual void set_next_arg(cmd_context & ctx, sexpr * n) { UNREACHABLE(); }
 };
 
 #endif

src/muz/rel/dl_base.h

@@ -871,6 +871,7 @@ namespace datalog {
 
     class table_row_mutator_fn {
     public:
+        virtual ~table_row_mutator_fn() {}
         /**
             \brief The function is called for a particular table row. The \c func_columns contains 
             a pointer to an array of functional column values that can be modified. If the function