sync: add explicit noCopy fields to Map, Mutex, and Once
Following CLs will refactor Mutex and change the internals of Map. This
ends up breaking tests in x/tools for the copylock vet check, because
the error message changes. Let's insulate ourselves from such things
permanently by adding an explicit noCopy field. We'll update the vet
check to accept that as the problem, rather than depend on less explicit
internals.
We capture Once here too to clean up the error message as well.
Change-Id: Iead985fc8ec9ef3ea5ff615f26dde17bb03aeadb
Reviewed-on: https://go-review.googlesource.com/c/go/+/627777 Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com> Reviewed-by: Tim King <taking@google.com>