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.
1c292035e1