Pull request https://github.com/SeanNaren/warp-ctc/pull/21 43 seems to have broken the process. I was stuck here for the past 2 hours too.
In warp-ctc checkout to a commit before that https://github.com/SeanNaren/warp-ctc/commit/432cf33910f1717b01f90d2662b575ab8de8fb6d 36.
git checkout 432cf33910f1717b01f90d2662b575ab8de8fb6d and build again. Should work.