C++: don't issue the definition of symbol_type when not used

Currently, in glr.cc, we emit the definitions of basic_symbol and
symbol_type, although there are not used.

* data/c++.m4 (b4_public_types_declare): Extract these definitions from
here, and move them...
(b4_symbol_type_declare): here.
(b4_public_types_declare): Also remove the definition of the symbol
constructors.
* data/lalr1.cc (b4_shared_declarations): Adjust: call
b4_symbol_type_declare and b4_symbol_constructor_declare.

data/c++.m4

@@ -192,8 +192,15 @@ m4_define([b4_public_types_declare],
 
     /// Internal symbol number for tokens (subsumed by symbol_number_type).
     typedef ]b4_int_type_for([b4_translate])[ token_number_type;
+]])
 
-    /// A complete symbol.
+
+# b4_symbol_type_declare
+# ----------------------
+# Define symbol_type, the external type for symbols used for symbol
+# constructors.
+m4_define([b4_symbol_type_declare],
+[[    /// A complete symbol.
     ///
     /// Expects its Base type to provide access to the symbol type
     /// via type_get().
@@ -281,8 +288,7 @@ m4_define([b4_public_types_declare],
 
     /// "External" symbols: returned by the scanner.
     typedef basic_symbol<by_type> symbol_type;
-
-]b4_symbol_constructor_declare])
+]])
 
 
 # b4_public_types_define(hh|cc)

data/lalr1.cc

@@ -176,6 +176,7 @@ b4_location_define])])[
   {
   public:
 ]b4_public_types_declare[
+]b4_symbol_type_declare[
     /// Build a parser object.
     ]b4_parser_class_name[ (]b4_parse_param_decl[);
     virtual ~]b4_parser_class_name[ ();
@@ -206,6 +207,8 @@ b4_location_define])])[
     /// Report a syntax error.
     void error (const syntax_error& err);
 
+]b4_symbol_constructor_declare[
+
   private:
     /// This class is not copyable.
     ]b4_parser_class_name[ (const ]b4_parser_class_name[&);