cmd/cgo: update outdated docs about cgocheck2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>

diff --git a/src/cmd/cgo/doc.go b/src/cmd/cgo/doc.go
index c2e375165c6731903225624d293a9beb52e4ee95..1c5d4b060d4fabf2d2d1139fdac23caf7b59f31e 100644 (file)
--- a/src/cmd/cgo/doc.go
+++ b/src/cmd/cgo/doc.go
@@ -402,7 +402,8 @@ controlled by the cgocheck setting of the GODEBUG environment
 variable. The default setting is GODEBUG=cgocheck=1, which implements
 reasonably cheap dynamic checks. These checks may be disabled
 entirely using GODEBUG=cgocheck=0. Complete checking of pointer
-handling, at some cost in run time, is available via GODEBUG=cgocheck=2.
+handling, at some cost in run time, is available by setting
+GOEXPERIMENT=cgocheck2 at build time.
 
 It is possible to defeat this enforcement by using the unsafe package,
 and of course there is nothing stopping the C code from doing anything