cmd/dist: mark openbsd-mips64 and openbsd-ppc64 broken

cmd/dist: mark openbsd-mips64 and openbsd-ppc64 broken

The former was broken deliberately; see #58110. The latter is just an
in-progress port.

Updates #58110, #56001.

Change-Id: I7f1c5e2ac016fb7c65c081174d19239fc9b1ea32
Reviewed-on: https://go-review.googlesource.com/c/go/+/482115
Auto-Submit: Heschi Kreinick <heschi@google.com>
TryBot-Bypass: Heschi Kreinick <heschi@google.com>
Run-TryBot: Heschi Kreinick <heschi@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>