internal/cpu: skip arm64 feature test on unsupported GOOS
internal/cpu: skip arm64 feature test on unsupported GOOS

Fixes #24753

Change-Id: Ic6049da98b8eee41223df71ffafa71a894915bd7
Reviewed-on: https://go-review.googlesource.com/105455
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
Run-TryBot: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

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