glr2.cc: example: style: add missing copyright headers

* examples/c++/glr/ast.hh, examples/c++/glr/c++-types.yy: here.
* examples/c++/glr/local.mk: Fix distribution of ast.hh.

examples/c++/glr/ast.hh

@@ -1,3 +1,20 @@
+/*
+  Copyright (C) 2020 Free Software Foundation, Inc.
+
+  This program is free software: you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation, either version 3 of the License, or
+  (at your option) any later version.
+
+  This program is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
 #include <iostream>
 
 #if __cplusplus < 201103L