cmd/dist: execute cgo_stdio and cgo_life as host tests

Now that these tests are written in Go, they must be run in host mode
in order to be able to exec `go run` as a subprocess.

Updates #30228

Change-Id: Ibedf86a8e18ae1b6f583c1bbdcb99d19c8e01744
Reviewed-on: https://go-review.googlesource.com/c/164137


Run-TryBot: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Elias Naur <mail@eliasnaur.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>