libgo: update to Go1.16.3 release

Change-Id: I5f73fa30d5e5865f59b7eb00204c6e5d7661fe21
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/309490
Trust: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>
20 files changed