net/mail: use sync.OnceValue to build dateLayouts
Simplify buildDateLayouts with sync.OnceValue.
Change-Id: Ib48ab20ee00f5e44cc1b0f6e1afe3fcd1b7dc3c7
GitHub-Last-Rev:
0866d463de1ec618d0d645b98f5e94917b8c3bde
GitHub-Pull-Request: golang/go#72743
Reviewed-on: https://go-review.googlesource.com/c/go/+/656055
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: David Chase <drchase@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>