Merge #17081: doc: fix Makefile target in benchmarking.md
a54ab2104c82c41d17ca603999a9a03161eefc9e [doc] fix Makefile target in benchmarking.md (Sebastian Falbesoner)
Pull request description:
While the resulting binary is called `bench_bitcoin`, the Makefile target is
named `bitcoin_bench` (see `src/Makefile.bench.include`)
ACKs for top commit:
ACK a54ab2104c82c41d17ca603999a9a03161eefc9e - Tested on macOS and Debian 9.9, as this only [seemed to work there](https://github.com/bitcoin/bitcoin/pull/16536#discussion_r310366868) when these docs were added.