test: move linkx and sinit to run.go

The remaining run-only tests will be migrated to run.go in another CL.

This CL will break the build due to issues 8746 and 8806.

Update issue 4139
Update issue 8746
Update issue 8806

LGTM=rsc
R=rsc, bradfitz, iant
CC=golang-codereviews
https://codereview.appspot.com/144630044

Committer: Russ Cox <rsc@golang.org>