cmd/go: add XCOFF format handler for go version
cmd/go: add XCOFF format handler for go version

Change-Id: Ib102ae95acfd89fc3c9942a4ec82c74362f62045
Reviewed-on: https://go-review.googlesource.com/c/go/+/174299
Run-TryBot: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

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