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 <bcmills@google.com>
Reviewed-by: Ayappan Perumal <ayappanec@gmail.com>
Auto-Submit: Bryan Mills <bcmills@google.com>
Reviewed-by: Russ Cox <rsc@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>

Since packages in "std" no longer have install targets, checking them
for staleness is somewhat meaningless: if they are not cached they
will be rebuilt anyway, and without installed archives against which
we can compare them the staleness check will not detect builder skew.

It would still be meaningful to check "cmd" for staleness, but
(especially on sharded VM-based builders) that is a fairly expensive
operation relative to its benefit. If we are really interested in
detecting builder skew and/or build reproducibility, we could instead
add a "misc" test (similar to "misc/reboot", or perhaps even a part of
that test) that verifies that bootstrapped binaries are reproducible.

For #57734.
Updates #47257.
Updates #56896.

Change-Id: I8683ee81aefe8fb59cce9484453df9729bdc587c
Reviewed-on: https://go-review.googlesource.com/c/go/+/452775
Run-TryBot: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Bryan Mills <bcmills@google.com>
Reviewed-by: Austin Clements <austin@google.com>

Since packages in "std" no longer have install targets, checking them
for staleness is somewhat meaningless: if they are not cached they
will be rebuilt anyway, and without installed archives against which
we can compare them the staleness check will not detect builder skew.

It would still be meaningful to check "cmd" for staleness, but
(especially on sharded VM-based builders) that is a fairly expensive
operation relative to its benefit. If we are really interested in
detecting builder skew and/or build reproducibility, we could instead
add a "misc" test (similar to "misc/reboot", or perhaps even a part of
that test) that verifies that bootstrapped binaries are reproducible.

For golang#57734.
Updates golang#47257.
Updates golang#56896.

Change-Id: I8683ee81aefe8fb59cce9484453df9729bdc587c
Reviewed-on: https://go-review.googlesource.com/c/go/+/452775
Run-TryBot: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Bryan Mills <bcmills@google.com>
Reviewed-by: Austin Clements <austin@google.com>