fix warnings

Signed-off-by: Nikolaj Bjorner <[email protected]>

src/ast/recfun_decl_plugin.h

@@ -60,7 +60,7 @@ namespace recfun {
         func_decl_ref       m_pred; //<! predicate used for this case
         expr_ref_vector     m_guards; //<! conjunction that is equivalent to this case
         expr_ref            m_rhs; //<! if guard is true, `f(t1...tn) = rhs` holds
-        def *               m_def; //<! definition this is a part of
+        def *               m_def = nullptr;; //<! definition this is a part of
         bool                m_immediate = false; //<! does `rhs` contain no defined_fun/case_pred?
 
         case_def(ast_manager& m):