cmd/dist: test cmd module on js/wasm

cmd/dist: test cmd module on js/wasm

Most tests will be skipped anyway because 'go build' is not available,
but this ensures cmd will be build tested by TryBots for js/wasm.

For #25911
For #35220
For #54219

Change-Id: I09c75905c36311810eb1ae75eeee2fa6102c1c0d
Reviewed-on: https://go-review.googlesource.com/c/go/+/435237
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>