sl: Fix OS X build (bison)

lib/hx509/sel-gram.y

@@ -78,6 +78,9 @@
 %token <string> STRING
 %token <string> IDENTIFIER
 
+%destructor { _hx509_expr_free($$); } expr comp word words number string function variable variables
+%destructor { free($$); } NUMBER STRING IDENTIFIER
+
 %left '!'
 %left kw_AND
 %left kw_OR