hash/crc32,hash/crc64: use sync.OnceFunc
Use sync.OnceFunc to simplify the code and to reduce global variables.
Change-Id: I7676339177e082c5be93dcf8121e379a6a7de912
GitHub-Last-Rev:
f796c49260ad19c33b616c9543b99f7f425dc2fe
GitHub-Pull-Request: golang/go#69633
Reviewed-on: https://go-review.googlesource.com/c/go/+/615920
Reviewed-by: David Chase <drchase@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>