Encapsulate code properties and related functionality for the various

destructors, printers, and actions into a code_props structure and
interface.
* src/location.h (EMPTY_LOCATION_INIT): Define so that it's easier to
consistently initialize const structs that have an empty location field.
* src/location.c (empty_location): Initialize with EMPTY_LOCATION_INIT
to ensure consistency.
* src/output.c (symbol_destructors_output, symbol_printers_output):
Replace with...
(symbol_code_props_output): ... this to eliminate duplicate code.
(output_skeleton): Update to use symbol_code_props_output.
* src/parse-gram.y (prologue_declaration, braceless, epilogue.opt):
Update all uses of translate_* functions to use the new code_props
interface and to use gram_scanner_last_string_free and
code_scanner_last_string_free where possible.
(grammar_declaration): symbol_list_destructor_set and
symbol_list_printer_set now perform the translation, so don't do it
here.  Use gram_scanner_last_string_free where possible.
* src/reader.c: Update to use code_props interface for destructors and
rule actions.
* src/scan-code.h (code_props): New structure.
(code_props_none_init, CODE_PROPS_NONE_INIT, code_props_none): New
function, macro, and const global variable for initializing a
code_props with no code.
(code_props_plain_init, code_props_symbol_action_init,
code_props_rule_action_init, code_props_translate_code,
code_props_code_get, code_props_location_get,
code_props_is_value_used): The rest of the new code_props interface.
(translate_rule_action, translate_symbol_action, translate_code):
Remove as these are now just special cases within
code_props_translate_code, which is switched on the code_props kind.
(code_scanner_last_string_free): New function similar to
gram_scanner_last_string_free.
* src/scan-code.l: Implement the new interface.
(last_string): New static global similar to the one in scan-gram.l.
(SC_SYMBOL_ACTION): For $$, set the is_value_used member of the
code_props since Bison will one day use this information for
destructors and printers.
(<*><<EOF>>): Use STRING_FINISH so that last_string is set.
(handle_action_dollar): Update to use the code_props interface of rule
actions.  Use symbol_list_n_get and set is_value_used directly since
symbol_list_n_used_set is removed.
* src/symlist.h, src/symlist.c (symbol_list): Replace action,
action_location, and used members with a code_props member, and update
all uses.
(symbol_list_n_used_set): Remove since it would need to break the
encapsulation of code_props.
(symbol_list_destructor_set, symbol_list_printer_set): Perform code
translation here rather than depending on the caller to do so.
* src/symtab.h (symbol, semantic_type): Remove destructor_location and
printer_location members and change the type of the destructor and
printer members to code_props.
(symbol_destructor_location_get, symbol_printer_location_get): Remove
unneeded.
(symbol_destructor_set, symbol_destructor_get, symbol_printer_set,
symbol_printer_get, semantic_type_destructor_set,
semantic_type_printer_set, default_tagged_destructor_set,
default_tagless_destructor_set, default_tagged_printer_set,
default_tagless_printer_set): Use code_props in arguments and return
types in place of const char * and location.
* src/symtab.c: Update implementation for interface and struct changes.
(default_tagged_destructor_location,
default_tagless_destructor_location, default_tagged_printer_location,
default_tagless_printer_location): Remove since we...
(default_tagged_destructor, default_tagless_destructor,
default_tagged_printer, default_tagless_printer): ... change the type
of these to code_props.
(SYMBOL_CODE_PRINT): New similar to SYMBOL_ATTR_PRINT but for
code_props members.
(symbol_print): Use SYMBOL_CODE_PRINT.

* src/scan-gram.h (gram_last_string): Remove declaration.
* src/scan-gram.l (last_string): Declare it static.

src/location.h

@@ -71,6 +71,7 @@ typedef struct
 
 #define YYLTYPE location
 
+#define EMPTY_LOCATION_INIT {{NULL, 0, 0}, {NULL, 0, 0}}
 extern location const empty_location;
 
 /* Set *LOC and adjust scanner cursor to account for token TOKEN of