Add riscv64a23 support
On Ubuntu, the latest Rust toolchain uses the RVA23 profile by default (riscv64a23-unknown-linux-gnu). The mozjs configuration files don't recognize that platform, so Ubuntu riscv64 builds FTBFS.
This change adds riscv64a23-unknown-linux-gnu as a recognized platform during configuration.
Edited by Jeremy Bícha