cmd/dist: correct default C++ compiler when using gcc
cmd/dist: correct default C++ compiler when using gcc

Fixes #22609

Change-Id: Ic948345e7d1623a7defee6a6493eb81fe7393111
Reviewed-on: https://go-review.googlesource.com/76396
Run-TryBot: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
Reviewed-by: David Crawshaw <a2f0bf29257797dd66800b4fbb9945c3e216c004@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

josharian/go,codestation/go,Cofyc/go,nawawi/go,CAFxX/go,akutz/go,cloudflare/go,josharian/go,CAFxX/go,christopher-henderson/Go,cloudflare/go,Cofyc/go,akutz/go,cloudflare/go,golang/go,golang/go,codestation/go,nawawi/go,Cofyc/go,codestation/go,cloudflare/go,nawawi/go,CAFxX/go,codestation/go,CAFxX/go,josharian/go,CAFxX/go,josharian/go,CAFxX/go,CAFxX/go,Cofyc/go,cloudflare/go,Cofyc/go,josharian/go,cloudflare/go,Cofyc/go,nawawi/go,akutz/go,codestation/go,nawawi/go,akutz/go,akutz/go,codestation/go,CAFxX/go,cloudflare/go,nawawi/go,josharian/go,cloudflare/go,golang/go,akutz/go,akutz/go,Cofyc/go,golang/go,golang/go,josharian/go,akutz/go,nawawi/go,codestation/go,nawawi/go,josharian/go,golang/go,codestation/go,golang/go,golang/go,Cofyc/go