x/website: build broken on freebsd-riscv64-unmatched due to outdated x/sys dependency

[bcmills]

https://build.golang.org/log/0577c687a5f6b6be718799bebf6564607fdfef23:

# golang.org/x/sys/unix
../../../../pkg/mod/golang.org/x/sys@v0.0.0-20211124211545-fe61309f8881/unix/sockcmsg_unix.go:34:9: undefined: Cmsghdr
../../../../pkg/mod/golang.org/x/sys@v0.0.0-20211124211545-fe61309f8881/unix/syscall_freebsd.go:54:9: undefined: RawSockaddrDatalink
../../../../pkg/mod/golang.org/x/sys@v0.0.0-20211124211545-fe61309f8881/unix/syscall_unix.go:186:38: undefined: _Socklen
../../../../pkg/mod/golang.org/x/sys@v0.0.0-20211124211545-fe61309f8881/unix/syscall_unix.go:193:7: undefined: RawSockaddrInet4
../../../../pkg/mod/golang.org/x/sys@v0.0.0-20211124211545-fe61309f8881/unix/syscall_unix.go:201:9: undefined: RawSockaddrInet6
../../../../pkg/mod/golang.org/x/sys@v0.0.0-20211124211545-fe61309f8881/unix/syscall_unix.go:207:7: undefined: RawSockaddrUnix
../../../../pkg/mod/golang.org/x/sys@v0.0.0-20211124211545-fe61309f8881/unix/cap_freebsd.go:19:23: undefined: CAP_RIGHTS_VERSION_00
../../../../pkg/mod/golang.org/x/sys@v0.0.0-20211124211545-fe61309f8881/unix/cap_freebsd.go:20:23: undefined: CAP_RIGHTS_VERSION_00
../../../../pkg/mod/golang.org/x/sys@v0.0.0-20211124211545-fe61309f8881/unix/cap_freebsd.go:47:21: undefined: CapRights
../../../../pkg/mod/golang.org/x/sys@v0.0.0-20211124211545-fe61309f8881/unix/cap_freebsd.go:51:24: undefined: CapRights
../../../../pkg/mod/golang.org/x/sys@v0.0.0-20211124211545-fe61309f8881/unix/cap_freebsd.go:51:24: too many errors
?   	golang.org/x/website/cmd/googlegolangorg	[no test files]
?   	golang.org/x/website/cmd/locktrigger	[no test files]
FAIL	golang.org/x/website/cmd/golangorg [build failed]

(CC @golang/riscv64)

[gopherbot]

Change https://go.dev/cl/456517 mentions this issue: all: update golang.org/x dependencies to latest

[gopherbot]

Change https://go.dev/cl/456655 mentions this issue: dashboard: skip x/website on freebsd/riscv64

[gopherbot]

Change https://go.dev/cl/457555 mentions this issue: dashboard: re-enable x/website on freebsd-riscv64-unmatched