As of writing (11.11.2021) building for risc-v considered to be highly experimental. Not all features can be enabled.
This is for the case when you have Linux machine and want to use it to build `clickhouse` binary that will run on another Linux machine with RISC-V 64 CPU architecture. This is intended for continuous integration checks that run on Linux servers.
The cross-build for RISC-V 64 is based on the [Build instructions](../development/build.md), follow them first.