cmd: merge branch 'dev.link' into master

In the dev.link branch we have continued developing the new object
file format support and the linker improvements described in
https://golang.org/s/better-linker . Since the last merge (May 1st
2020), more progress has been made to improve the new linker, with
improvements on both linker speed and memory usage.

Fixes #40703.

Change-Id: I9924ea88d981845c3a40ec8c25820120fc21c003