luci: request xcode 9e501 + associated caches on mac_upload_clang.

Bug: 731375
Change-Id: I0bcdc83ee401d093a725b219dc26956982895ce6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1628932
Reviewed-by: Nico Weber <thakis@chromium.org>
Reviewed-by: Ben Pastene <bpastene@chromium.org>
Commit-Queue: John Budorick <jbudorick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#663322}
1 file changed