On darwin, /tmp and /var directories are usually linked to /private.

% cd $TMPDIR; pwd -L
/var/.../T
% pwd -P
/private/var/.../T

Change-Id: I277ff2d096344d9a80e6004a83e9fc3e1716348c
Reviewed-on: https://go-review.googlesource.com/8842Reviewed-by: David Crawshaw <crawshaw@golang.org>