cmd/dist: skip the staleness check for 'cmd' when testing on aix-ppc64
cmd/dist: skip the staleness check for 'cmd' when testing on aix-ppc64

The gcc toolchain on the aix-ppc64 builder apparently does not achieve
reproducible builds for packages that use cgo, which causes the
binaries in cmd that use package "net" (cmd/go, cmd/pprof, and
cmd/trace) to appear stale whenever the Go build cache is cleared.

For now, we work around the staleness by rebuilding std and simply not
checking whether cmd is stale.

For #56896.
Updates #47257.

Change-Id: I15f86e72dee53904b881710d5d5d613872361510
Reviewed-on: https://go-review.googlesource.com/c/go/+/452680
Run-TryBot: Bryan Mills <1c8aad60184261ccede67f5c63a0d2a3bf3c9ff4@google.com>
Reviewed-by: Ayappan Perumal <a342b0048ab8300b89c4a655343427a5adfcb749@gmail.com>
Auto-Submit: Bryan Mills <1c8aad60184261ccede67f5c63a0d2a3bf3c9ff4@google.com>
Reviewed-by: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

golang/go,golang/go,golang/go,golang/go,golang/go,golang/go,golang/go,golang/go