cmd/go/internal/cfg: note the copy of this code in x/tools/cmd/godoc
cmd/go/internal/cfg: note the copy of this code in x/tools/cmd/godoc

Updates #23445

Change-Id: I4b09073e53b1cf04de698b711fb5fb0d08bc02df
Reviewed-on: https://go-review.googlesource.com/118077
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

nawawi/go,cloudflare/go,akutz/go,josharian/go,nawawi/go,golang/go,golang/go,CAFxX/go,CAFxX/go,akutz/go,josharian/go,akutz/go,CAFxX/go,josharian/go,cloudflare/go,CAFxX/go,CAFxX/go,golang/go,CAFxX/go,nawawi/go,golang/go,josharian/go,nawawi/go,cloudflare/go,akutz/go,cloudflare/go,nawawi/go,nawawi/go,cloudflare/go,akutz/go,golang/go,nawawi/go,akutz/go,CAFxX/go,josharian/go,cloudflare/go,josharian/go,CAFxX/go,cloudflare/go,golang/go,josharian/go,golang/go,cloudflare/go,akutz/go,josharian/go,akutz/go,golang/go,nawawi/go