printer/destructor: translate only once

Currently "%printer {...} a b c d e f" translates the {...} six times.
Not only is this bad for time and space, it also issues six times the
same warnings.

* src/symlist.h, src/symlist.c (symbol_list_destructor_set)
(symbol_list_printer_set): Take the action as code_props instead of
const char *.
* src/parse-gram.y: Translate these actions here.
* src/scan-code.h: Comment change.
* tests/input.at: Check that warnings are issued only once.

tests/input.at

@@ -1377,13 +1377,16 @@ AT_CLEANUP
 
 AT_SETUP([[Stray $ or @]])
 
+# Give %printer and %destructor "<*> exp TOK" instead of "<*>" to
+# check that the warnings are reported once, not three times.
+
 AT_DATA_GRAMMAR([[input.y]],
 [[%token TOK
-%destructor     { $%; @%; } <*>;
+%destructor     { $%; @%; } <*> exp TOK;
 %initial-action { $%; @%; };
-%printer        { $%; @%; } <*>;
+%printer        { $%; @%; } <*> exp TOK;
 %%
-exp: TOK        { $%; @%; };
+exp: TOK        { $%; @%; $$ = $1; };
 ]])
 
 AT_BISON_CHECK([[input.y]], 0, [],