RISC-V port

[Tom Tromey]

Stefan> I am interested in being the responsible party to get this code into a
Stefan> mergable condition.  I am familiar with the RISC-V ISA and calling
Stefan> convention and with libffi's broad principles of operation, but not
Stefan> with the details of libffi internals.

Stefan> How shall we proceed?

I think the best thing to do is, first, make sure the port passes the
test suite; and, second, submit a PR on github.  Any necessary review
can be done there.

Tom