Failures here don't otherwise affect the build, but they do cause a
slow file leak in the user's temp directory. The user deserves at
least a cursory warning that something may be amiss.
Updates #30789
Change-Id: Id0e72b1967e7f7c88cdc94d532554496653f264b
Reviewed-on: https://go-review.googlesource.com/c/go/+/171764
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>
ccaa491386