In this particular context, they're trying to run code compiled for x86_64 on RISCV5. The need from "we just need a few more instructions to get feature parity" comes from trying to run code that is already compiled for an architecture with all those extra instructions.

In theory, if you compiled the original _source_ code for RISC, you'd get an entirely binary and wouldn't need those specific instructions.

In practice, I doubt anyone is going to actually compile these games for RISCV5.