For some reason I decided to change the argument passing order before
submitting my PR, but this would cause the oldset argument to always
be 0x74 as a0 is overridden with 0 in that order.
This is a minimal set of changes to allow `serenity.sh build riscv64` to
successfully generate the build environment and start building. This
includes some, but not all, assembly stubs that will be needed later on;
they are currently empty.
