Still happens, not that we care that much about our package.py log size:
https://ci.chromium.org/buildbot/tryserver.chromium.win/win_upload_clang/370

[433/4123] Building CXX object projects\compiler-rt\lib\sanitizer_common\CMakeFiles\RTSanitizerCommon.x86_64.dir\sanitizer_deadlock_detector2.cc.obj
clang-cl.exe: warning: unknown argument ignored in clang-cl: '-std=c++11' [-Wunknown-argument]
clang-cl.exe: warning: unknown argument ignored in clang-cl: '-std=c++11' [-Wunknown-argument]
clang-cl.exe: warning: unknown argument ignored in clang-cl: '-fno-exceptions' [-Wunknown-argument]
clang-cl.exe: warning: unknown argument ignored in clang-cl: '-fomit-frame-pointer' [-Wunknown-argument]
clang-cl.exe: warning: unknown argument ignored in clang-cl: '-funwind-tables' [-Wunknown-argument]
clang-cl.exe: warning: unknown argument ignored in clang-cl: '-fno-stack-protector' [-Wunknown-argument]
clang-cl.exe: warning: unknown argument ignored in clang-cl: '-fvisibility=hidden' [-Wunknown-argument]
clang-cl.exe: warning: unknown argument ignored in clang-cl: '-fno-lto' [-Wunknown-argument]
clang-cl.exe: warning: unknown argument ignored in clang-cl: '-fno-rtti' [-Wunknown-argument

Nice, I didn't know a cmake update fixes this! I'm getting this all the time locally as well :-D

I started looking at this. The upstream cmake package for Linux won't run with the libstdc++ version we're using in update.py, so I'm trying a patch to just use the default libstdc++ here: https://chromium-review.googlesource.com/c/chromium/src/+/1183915

If that sticks, I have a patch to move to the latest cmake version.

The cmake patch is here: https://chromium-review.googlesource.com/c/chromium/src/+/1187160

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/0546b3534632dcc649027d016e70164b00a86aaa

commit 0546b3534632dcc649027d016e70164b00a86aaa
Author: Hans Wennborg <hans@chromium.org>
Date: Fri Aug 24 19:51:07 2018

Clang: stop building with GCC/libstdc++ from Ubuntu Precise

Previously we used a GCC/libstdc++ package from Ubuntu Precise to build a Clang
that would work on Precise or later. These days, all bots and developers are on
Trusty or later, so this should no longer be necessary.

Besides simplifying things, this allows us to easier move to using the
latest CMake when building Clang, because it was built with a newer
libstdc++ than the Precise one.

Bug:  797991 
Change-Id: I528825389241f60ccc96167015370cd5e285725d
Reviewed-on: https://chromium-review.googlesource.com/1188679
Reviewed-by: Reid Kleckner <rnk@chromium.org>
Commit-Queue: Hans Wennborg <hans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#585953}
[modify] https://crrev.com/0546b3534632dcc649027d016e70164b00a86aaa/tools/clang/scripts/update.py

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/814930c5133aacaf7310960087927374a8e514ea

commit 814930c5133aacaf7310960087927374a8e514ea
Author: Hans Wennborg <hans@chromium.org>
Date: Fri Aug 24 20:36:32 2018

Clang update script: use a newer CMake

This depends on https://chromium-review.googlesource.com/c/chromium/src/+/1188679

Bug:  797991 
Change-Id: I81f648d269152eafbb6208d0c831e2d14511fc0c
Reviewed-on: https://chromium-review.googlesource.com/1187160
Commit-Queue: Hans Wennborg <hans@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#585976}
[modify] https://crrev.com/814930c5133aacaf7310960087927374a8e514ea/tools/clang/scripts/update.py

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/536bb7d3cf643f606bc91678a1fcaf4077f76f99

commit 536bb7d3cf643f606bc91678a1fcaf4077f76f99
Author: Reid Kleckner <rnk@google.com>
Date: Fri Aug 24 23:32:37 2018

Fix path to CMake bin directory in update.py

There is no extra 'cmake' path component after bin on Linux.
Hopefully this will resurrect the Linux Clang ToT bots after
https://crrev.com/585976.

TBR=hans@chromium.org
NOTRY=True

Bug:  797991 
Change-Id: I7e1e38e824c8986303a9ec1972bb5f57a2cd9bea
Reviewed-on: https://chromium-review.googlesource.com/1189034
Reviewed-by: Reid Kleckner <rnk@chromium.org>
Commit-Queue: Reid Kleckner <rnk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#586051}
[modify] https://crrev.com/536bb7d3cf643f606bc91678a1fcaf4077f76f99/tools/clang/scripts/update.py