cmd/link: unskip TestBuildForTvOS on dwarin/arm64

cmd/link: unskip TestBuildForTvOS on dwarin/arm64

TestBuildForTvOS currently runs only on darwin/amd64. It can also
run on darwin/arm64, if the SDK is installed. Unskip the test.

Also add logging for the build commands it runs.

For #63203.

Change-Id: Id41d2e1879f5d39d239f0586d836d33accf5efbf
Reviewed-on: https://go-review.googlesource.com/c/go/+/531555
Reviewed-by: Than McIntosh <thanm@google.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>