add ~riscv keyword
Looks good on riscv USE tests started on Tue Nov 1 16:38:56 -00 2022 FEATURES=' test' USE='' succeeded for =net-proxy/wwwoffle-2.9i-r2 USE='gnutls ipv6 -zlib' succeeded for =net-proxy/wwwoffle-2.9i-r2
riscv done all arches done