rvvm: Add RVVM recipe
This MR adds a recipe to build RVVM (RISC-V Virtual Machine).
Tested features:
- GUI (Via SDL1, other backends are not working well due to lack of dynamic linking)
- JIT (Full guest acceleration)
Disabled features:
- Building librvvm (Due to lack of dynamic linking)
- Userland networking (Something in Redox causes RVVM networking stack to hang)