riscv: add `allocReg` helper, and clean up some comparing logic
- Added the basic framework for panicing with an overflow in `airAddWithOverflow`, but there is no check done yet.
- added the `cmp_lt`, `cmp_gte`, and `cmp_imm_eq` MIR instructions, and their respective functionality.
09b7aabe09David Rubin committed on 5/11/2024, 9:17:11 AMparent08452b1