riscv64gc-unknown-linux-gnu is Tier 2 for cross-compilation but not for hosts.
There is discussion on this here https://github.com/rust-lang/rust/pull/72973
To move forward with RISC-V GNU/Linux host support, the compiler team would like at least two people to form a RISC-V notification group. I am willing to do this but we need at least one other volunteer.
Would anybody else be interested?
(The builder for the host binaries is also pending approval from the infrastructure team).