It triggers for all go versions before 1.11. We thought we might
be able to backport some of the necessary changes to 1.10.4, but
it was infeasible, so no 1.10.x versions will support the non-fallback
behavior.
Change-Id: Ib22be2715bf504464e4bd09c14453e5d132776f3
Reviewed-on: https://go-review.googlesource.com/c/156898
Reviewed-by: Ian Lance Taylor <iant@golang.org>