c++: add copy ctors for compatibility with the IAR compiler

Reported by Andreas Damm.
https://savannah.gnu.org/support/?110032

* data/skeletons/lalr1.cc (stack_symbol_type::operator=): New
overload, const, to please the IAR C++ compiler (version ca 2013).

THANKS

@@ -10,6 +10,7 @@ Albert Chin-A-Young       china@thewrittenword.com
 Alexander Belopolsky      alexb@rentec.com
 Alexandre Duret-Lutz      adl@lrde.epita.fr
 Andre da Costa Barros     andre.cbarros@yahoo.com
+Andreas Damm              adamm@onica.com
 Andreas Schwab            schwab@suse.de
 Andrew Suffield           asuffield@users.sourceforge.net
 Angelo Borsotti           angelo.borsotti@gmail.com

data/skeletons/lalr1.cc

@@ -335,6 +335,10 @@ m4_define([b4_shared_declarations],
       /// Assignment, needed by push_back by some old implementations.
       /// Moves the contents of that.
       stack_symbol_type& operator= (stack_symbol_type& that);
+
+      /// Assignment, needed by push_back by other implementations.
+      /// Needed by some other old implementations.
+      stack_symbol_type& operator= (const stack_symbol_type& that);
 #endif
     };
 
@@ -627,6 +631,17 @@ m4_if(b4_prefix, [yy], [],
   }
 
 #if YY_CPLUSPLUS < 201103L
+  ]b4_parser_class[::stack_symbol_type&
+  ]b4_parser_class[::stack_symbol_type::operator= (const stack_symbol_type& that)
+  {
+    state = that.state;
+    ]b4_variant_if([b4_symbol_variant([that.type_get ()],
+                                      [value], [copy], [that.value])],
+                   [[value = that.value;]])[]b4_locations_if([
+    location = that.location;])[
+    return *this;
+  }
+
   ]b4_parser_class[::stack_symbol_type&
   ]b4_parser_class[::stack_symbol_type::operator= (stack_symbol_type& that)
   {