meson: also override cppzmq dependency if draft API required
Follow-up for !187 (merged)
If we need to fallback for libzmq, we also need to fallback for cppzmq, otherwise system cppzmq uses the flags from system libzmq.
Follow-up for !187 (merged)
If we need to fallback for libzmq, we also need to fallback for cppzmq, otherwise system cppzmq uses the flags from system libzmq.