glr2.cc: example: use objects (not pointers) to represent the AST

Currently we are using pointers.  The whole point of
glr2.cc (vs. glr.cc) is precisely to allow genuine C++ objects to be
semantic values.  Let's make that work.

* data/skeletons/glr2.cc (glr_state::glr_state): Be sure to initialize
yysval.
(glr_state): Add copy-ctor, assignment and dtor.
(glr_state::copyFrom): Be sure to initialize the destination if it was
not.
(glr_state::~glr_state): Destroy the semantic value.
* examples/c++/glr/ast.hh: Rewrite so that we use genuine objects,
rather than a traditional OOP hierarchy that requires to deal with
pointers.
With help from Bruno Belanyi <bruno.belanyi@epita.fr>.
* examples/c++/glr/c++-types.yy: Remove memory management.
Use true objects.
(main): Don't reach yydebug directly.

* examples/c++/glr/local.mk: We need C++11.

examples/c++/glr/local.mk

@@ -34,7 +34,7 @@ CLEANDIRS += %D%/*.dSYM
 # Avoid using BUILT_SOURCES which is too global.
 $(%C%_c___types_OBJECTS): $(cxx_types_sources_generated)
 
-if ENABLE_CXX
+if ENABLE_CXX14
   check_PROGRAMS += %D%/c++-types
   dist_%C%_c___types_SOURCES =			\
     %D%/ast.hh
@@ -43,6 +43,7 @@ if ENABLE_CXX
     %D%/c++-types.hh
   # Don't use gnulib's system headers.
   %C%_c___types_CPPFLAGS = -I$(top_srcdir)/%D% -I$(top_builddir)/%D%
+  %C%_c___types_CXXFLAGS = $(CXX14_CXXFLAGS) $(WARN_CXXFLAGS_TEST)
   TESTS += %D%/c++-types.test
-endif ENABLE_CXX
+endif ENABLE_CXX14
 EXTRA_DIST += %D%/c++-types.yy %D%/c++-types.test