cmd/cgo: clarify that strings and slices may contain C pointers
Fixes #68832
Change-Id: I74b6aad9a18953c263cbbe795268017a72261f7f
Reviewed-on: https://go-review.googlesource.com/c/go/+/604715 Reviewed-by: Cherry Mui <cherryyz@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> Reviewed-by: Carlos Amedee <carlos@golang.org>
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