cmd: merge branch 'dev.link' into master

In the dev.link branch we continued developing the new object
file format support and the linker improvements described in
https://golang.org/s/better-linker . Since the last merge, more
progress has been made to improve the new linker.

This is a clean merge, as we already merged master branch to
dev.link first.

Change-Id: I1fef2b1d94bd2410001142da8991544da5ee896d