clang: current_exception_as_future must be in namespaced
clang: current_exception_as_future must be in namespaced

explicit instantiation of 'seastar::internal::current_exception_as_future'
must occur in namespace 'internal'

Signed-off-by: Alexander Gallego <60c6d277a8bd81de7fdde19201bf9c58a3df08f4@vectorized.io>
Message-Id: <20200109020840.1308555-1-60c6d277a8bd81de7fdde19201bf9c58a3df08f4@vectorized.io>

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