gem install memcached ではまったメモ

Error: $gem install memcached ... rlibmemcached_wrap.c: In function ‘_wrap_MemcachedSt_sasl_callbacks_set’: rlibmemcached_wrap.c:6669: error: ‘sasl_callback_t’ undeclared (first use in this function) rlibmemcached_wrap.c:6669: error: (Each undeclared identifier is reported only once rlibmemcached_wrap.c:6669: error: for…