Merge remote-tracking branch 'origin/maint'

* origin/maint:
  glr.cc: fix a clang warning
  maint: update copyright years
  build: fix VPATH issue
  build: avoid clang's colored diagnostics in the test suite
  tests: please clang and use ".cc", not ".c", for C++ input
  gnulib: update
  skeletons: avoid empty switch constructs
  lalr1.cc: fix compiler warnings
  yacc.c: do not use __attribute__ unprotected
  tests: style changes

data/stack.hh

@@ -72,6 +72,12 @@ m4_define([b4_stack_define],
         seq_.pop_back ();
     }
 
+    void
+    clear ()
+    {
+      seq_.clear ();
+    }
+
     inline
     typename S::size_type
     size () const
@@ -94,6 +100,8 @@ m4_define([b4_stack_define],
     }
 
   private:
+    stack (const stack&);
+    stack& operator= (const stack&);
     /// The wrapped container.
     S seq_;
   };