skeletons: use symbol(-2, kind)

Not all the symbols have a fixed symbol code.  UNDEF's one is fixed:
-2.

* data/skeletons/glr.c, data/skeletons/lalr1.cc, data/skeletons/lalr1.d,
* data/skeletons/yacc.c: here.

data/skeletons/glr.c

@@ -2132,7 +2132,7 @@ static yysymbol_kind_t
 yypcontext_token (const yyGLRStack *yystackp)
 {
   YYUSE (yystackp);
-  yysymbol_kind_t yytoken = yychar == ]b4_symbol(-2, id)[ ? ]b4_symbol_prefix[YYEMPTY : YYTRANSLATE (yychar);
+  yysymbol_kind_t yytoken = yychar == ]b4_symbol(-2, id)[ ? ]b4_symbol(-2, kind)[ : YYTRANSLATE (yychar);
   return yytoken;
 }
 
@@ -2151,7 +2151,7 @@ yypcontext_location (const yyGLRStack *yystackp)
 yy_syntax_error_arguments (const yyGLRStack* yystackp,
                            yysymbol_kind_t yyarg[], int yyargn)
 {
-  yysymbol_kind_t yytoken = yychar == ]b4_symbol(-2, id)[ ? ]b4_symbol_prefix[YYEMPTY : YYTRANSLATE (yychar);
+  yysymbol_kind_t yytoken = yychar == ]b4_symbol(-2, id)[ ? ]b4_symbol(-2, kind)[ : YYTRANSLATE (yychar);
   /* Actual size of YYARG. */
   int yycount = 0;
   /* There are many possibilities here to consider:
@@ -2182,7 +2182,7 @@ yy_syntax_error_arguments (const yyGLRStack* yystackp,
        one exception: it will still contain any token that will not be
        accepted due to an error action in a later state.]])[
   */
-  if (yytoken != ]b4_symbol_prefix[YYEMPTY)
+  if (yytoken != ]b4_symbol(-2, kind)[)
     {
       int yyn;
       if (yyarg)

data/skeletons/lalr1.cc

@@ -377,7 +377,7 @@ m4_define([b4_shared_declarations],
       void move (by_state& that);
 
       /// The symbol kind (corresponding to \a state).
-      /// \a ]b4_symbol_prefix[YYEMPTY when empty.
+      /// \a ]b4_symbol(-2, kind)[ when empty.
       symbol_kind_type type_get () const YY_NOEXCEPT;
 
       /// The state number used to denote an empty symbol.
@@ -700,7 +700,7 @@ b4_parse_error_case([verbose], [[
   ]b4_parser_class[::by_state::type_get () const YY_NOEXCEPT
   {
     if (state == empty_state)
-      return symbol_kind::]b4_symbol_prefix[YYEMPTY;
+      return symbol_kind::]b4_symbol(-2, kind)[;
     else
       return YY_CAST (symbol_kind_type, yystos_[+state]);
   }
@@ -725,7 +725,7 @@ b4_parse_error_case([verbose], [[
     b4_symbol_variant([that.type_get ()],
                       [value], [move], [YY_MOVE (that.value)])])[
     // that is emptied.
-    that.type = symbol_kind::]b4_symbol_prefix[YYEMPTY;
+    that.type = symbol_kind::]b4_symbol(-2, kind)[;
   }
 
 #if YY_CPLUSPLUS < 201103L

data/skeletons/lalr1.d

@@ -430,7 +430,7 @@ b4_locations_if([, ref ]b4_location_type[ yylocationp])[)
   {
     /// Lookahead and lookahead in internal form.
     int yychar = TokenKind.YYEMPTY;
-    SymbolKind yytoken = SymbolKind.]b4_symbol_prefix[YYEMPTY;
+    SymbolKind yytoken = SymbolKind.]b4_symbol(-2, kind)[;
 
     /* State.  */
     int yyn = 0;
@@ -574,7 +574,7 @@ m4_popdef([b4_at_dollar])])dnl
         {
           ++yynerrs_;
           if (yychar == TokenKind.YYEMPTY)
-            yytoken = SymbolKind.]b4_symbol_prefix[YYEMPTY;
+            yytoken = SymbolKind.]b4_symbol(-2, kind)[;
           yyerror (]b4_locations_if([yylloc, ])[yysyntax_error (yystate, yytoken));
         }
 
@@ -712,7 +712,7 @@ m4_popdef([b4_at_dollar])])dnl
          will still contain any token that will not be accepted due
          to an error action in a later state.
       */
-    if (tok != SymbolKind.]b4_symbol_prefix[YYEMPTY)
+    if (tok != SymbolKind.]b4_symbol(-2, kind)[)
     {
       // FIXME: This method of building the message is not compatible
       // with internationalization.

data/skeletons/yacc.c

@@ -1351,7 +1351,7 @@ yy_syntax_error_arguments (const yypcontext_t *yyctx,
        one exception: it will still contain any token that will not be
        accepted due to an error action in a later state.]])[
   */
-  if (yyctx->yytoken != ]b4_symbol_prefix[YYEMPTY)
+  if (yyctx->yytoken != ]b4_symbol(-2, kind)[)
     {
       int yyn;]b4_lac_if([[
       YYDPRINTF ((stderr, "Constructing syntax error message\n"));]])[
@@ -1582,7 +1582,7 @@ yyparse (]m4_ifset([b4_parse_param], [b4_formals(b4_parse_param)], [void])[)]])[
   /* The return value of yyparse.  */
   int yyresult;
   /* Lookahead token as an internal (translated) token number.  */
-  yysymbol_kind_t yytoken = ]b4_symbol_prefix[YYEMPTY;
+  yysymbol_kind_t yytoken = ]b4_symbol(-2, kind)[;
   /* The variables used to return semantic value and location from the
      action routines.  */
   YYSTYPE yyval;]b4_locations_if([[
@@ -1895,7 +1895,7 @@ yyreduce:
 yyerrlab:
   /* Make sure we have latest lookahead translation.  See comments at
      user semantic actions for why this is necessary.  */
-  yytoken = yychar == ]b4_symbol(-2, id)[ ? ]b4_symbol_prefix[YYEMPTY : YYTRANSLATE (yychar);
+  yytoken = yychar == ]b4_symbol(-2, id)[ ? ]b4_symbol(-2, kind)[ : YYTRANSLATE (yychar);
   /* If not already recovering from an error, report this error.  */
   if (!yyerrstatus)
     {