Fixes#16241
I made 64 bits op on 32 bits arches still leak since it was kinda promised.
The promised leaks were wider than this but I don't belive it's effect can
be observed in an breaking maner without using unsafe the way it's currently
setup.
Change-Id: I66d8df47bfe49bce3efa64ac668a2a55f70733a3
Reviewed-on: https://go-review.googlesource.com/c/go/+/462298
Reviewed-by: Mauri de Souza Meneguzzo <mauri870@gmail.com>
Reviewed-by: Keith Randall <khr@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
