This bug is very likely upstream bug #5237 [1] which has been solved since version 3.3.5. So packaging the current version (3.3.6) should be enough to get rid of it. I did it myself and it built fine in a current sid chroot, whereas 3.3.4 failed with the compiler error above.
Regards BZ [1] https://github.com/qbittorrent/qBittorrent/issues/5237
