noncopyable_function: Avoid uninitialized warning on empty types
noncopyable_function: Avoid uninitialized warning on empty types

Instead of disabling the warning, avoid copying the unused byte of
empty types.

Signed-off-by: Rafael Ávila de Espíndola <1975039f9046bf513b77c0c5639a0efc25f00e7f@scylladb.com>
Message-Id: <20191129180555.73053-1-1975039f9046bf513b77c0c5639a0efc25f00e7f@scylladb.com>

dreamsxin/seastar,cloudius-systems/seastar,syuu1228/seastar,scylladb/seastar,scylladb/seastar,syuu1228/seastar,avikivity/seastar,dreamsxin/seastar,dreamsxin/seastar,cloudius-systems/seastar,avikivity/seastar,scylladb/seastar,avikivity/seastar,cloudius-systems/seastar,syuu1228/seastar