cmd/go: accept -mcmodel and -mlarge-data-threshold compiler flags
For #67475
Change-Id: Ia90952eb7c19764306205928ead50bff22857378
Reviewed-on: https://go-review.googlesource.com/c/go/+/586675
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Ian Lance Taylor <iant@golang.org> Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com> Reviewed-by: Than McIntosh <thanm@google.com>