clang package script: Upload buildlog as separate file.

Currently, every clang package contains a buildlog.txt that's ~7MB.
It compresses well, and after #656764 it will be less than half the size,
but there's still no need for all devs and bots to download this data.
Upload it to a (gzip-compressed) separate file 'clang-12345-buildlog.txt'
instead.

While here, remove unreferenced function GsutilArchiveExists().

Also pass `args.update` instead of `args` as first argument of
MaybeUpload(), so the function doesn't have two separate `args`
parameters.

Bug: none
Change-Id: I5a3a9aa4ad2af17bd3fad19d11a64a66720ea9e1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1596351
Commit-Queue: Nico Weber <thakis@chromium.org>
Reviewed-by: Hans Wennborg <hans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#656979}
3 files changed