cmd/cgo: update outdated docs about cgocheck2
Setting GODEBUG=cgocheck=2 now panics with a message
such as "fatal error: cgocheck > 1 mode is no longer supported at runtime.
Use GOEXPERIMENT=cgocheck2 at build time instead."
Change-Id: If9a5a96933973e14a1a60b8e9fb6a1f4a818cf59
GitHub-Last-Rev:
787d62454c31565d0828777bf5ba24c99345af4d
GitHub-Pull-Request: golang/go#65224
Reviewed-on: https://go-review.googlesource.com/c/go/+/557597
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: qiulaidongfeng <2645477756@qq.com>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>