Compilation error with clang++ 3.9.1

Compilation with clang++ 3.9.1 fails with :

escape.cc:70:11: error: use of the 'fallthrough' attribute is a C++1z extension [-Werror,-Wc++1z-extensions]
          SPOT_FALLTHROUGH;
          ^
../../spot/misc/common.hh:132:32: note: expanded from macro 'SPOT_FALLTHROUGH'
#    define SPOT_FALLTHROUGH [[fallthrough]]
                               ^
escape.cc:153:15: error: use of the 'fallthrough' attribute is a C++1z extension [-Werror,-Wc++1z-extensions]
              SPOT_FALLTHROUGH;
              ^
../../spot/misc/common.hh:132:32: note: expanded from macro 'SPOT_FALLTHROUGH'
#    define SPOT_FALLTHROUGH [[fallthrough]]
                           ^