time, cmd/compile: backport fixes to 1.7.5

[josharian]

Reminder issue so that these come up in the 1.7.5 milestone. Per golang-dev thread, consider backporting fixes for issues #17276 and #18410 for 1.7.5.

[bradfitz]

I think I did both of those already:

https://go-review.googlesource.com/q/status:merged+branch:release-branch.go1.7

[josharian]

Indeed, sorry.