cmd/dist: do not run on ppc64le

cmd/dist: do not run on ppc64le

Also don't run on all the other tiny slow boxes we have.
Should fix the remaining ppc64le broken builders.

For #44505 (or at least somehow provoked by it).

Change-Id: I72e8086cb641f3f7da3a872140a752bf328eec1f
Reviewed-on: https://go-review.googlesource.com/c/go/+/421438
Reviewed-by: Heschi Kreinick <heschi@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>