cmd/dist: reject accidental use of internal packages from bootstrap toolchain
The compiler was accidentally using internal/godebug from
the Go 1.20 bootstrap toolchain and didn't get the behavior
it expected. Generalizing, we should never assume we know
the behavior of an internal package from an earlier bootstrap
toolchain, so disallow that case in cmd/dist.
Change-Id: I41e079f6120f4081124619bbe2b30069c96b9f29
Reviewed-on: https://go-review.googlesource.com/c/go/+/581496 Reviewed-by: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Russ Cox <rsc@golang.org>