GitLab

If TMPDIR is not set, the iOS runtime will automatically set TMPDIR
to a valid app temporary path.

For the iOS builders.

Change-Id: Ia82404059dcb10678f0a6e0c96d5efc79a5485fd
Reviewed-on: https://go-review.googlesource.com/110956


Run-TryBot: Elias Naur <elias.naur@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>