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/glr.c

@@ -246,13 +246,6 @@ b4_percent_code_get[]dnl
 # endif
 #endif
 
-/* Suppress unused-variable warnings by "using" E.  */
-#ifdef __GNUC__
-# define YYUSE(E) ((void) (E))
-#else
-# define YYUSE(E) /* empty */
-#endif
-
 #ifndef YYFREE
 # define YYFREE free
 #endif
@@ -281,17 +274,7 @@ b4_percent_code_get[]dnl
 # define YYLONGJMP(Env, Val) (longjmp (Env, Val), YYASSERT (0))
 #endif
 
-/*-----------------.
-| GCC extensions.  |
-`-----------------*/
-
-#ifndef __attribute__
-/* This feature is available in gcc versions 2.5 and later.  */
-# if (! defined __GNUC__ || __GNUC__ < 2 \
-      || (__GNUC__ == 2 && __GNUC_MINOR__ < 5))
-#  define __attribute__(Spec) /* empty */
-# endif
-#endif
+]b4_attribute_define[
 
 #ifndef YYASSERT
 # define YYASSERT(Condition) ((void) ((Condition) || (abort (), 0)))