First change: https://chromium-review.googlesource.com/c/577404/

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/cb4c0fbcccbcb44ea837a6b5b030d48ef84e9347

commit cb4c0fbcccbcb44ea837a6b5b030d48ef84e9347
Author: Hans Wennborg <hans@chromium.org>
Date: Wed Jul 19 12:22:50 2017

Clang build script config: the trunk version is now 6.0.0

Bug:  746303 
Change-Id: Iaa8b1a19011d9ff427763f47b7137612120cf278
Reviewed-on: https://chromium-review.googlesource.com/577404
Commit-Queue: Hans Wennborg <hans@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#487831}
[modify] https://crrev.com/cb4c0fbcccbcb44ea837a6b5b030d48ef84e9347/build/toolchain/toolchain.gni
[modify] https://crrev.com/cb4c0fbcccbcb44ea837a6b5b030d48ef84e9347/tools/clang/scripts/update.py

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/1c688af81fcfa4c072dcca79e698641839e8a42f

commit 1c688af81fcfa4c072dcca79e698641839e8a42f
Author: Nico Weber <thakis@chromium.org>
Date: Mon Jul 24 11:25:28 2017

Roll clang 307486:308728.

Ran `tools/clang/scripts/upload_revision.py 308728`.

This changes the clang version from 5.0.0 to 6.0.0, so simplify
some things that dealt with both numbers.

This changes clang to no longer look for libc++ headers in the
Fuchsia SDK.  To keep things building, use "our" libc++, like
on linux (use_custom_libcxx).  This in turn means we pass
-nodefaultlibs to the linker, which sadly also disables the
automatic linking of clang_rt.builtins, so do that manually now.
(In exchange, we no longer need to pass in -resource-dir.)

This makes -Wformat fire in Google Toolbox for Mac in iOS builds,
so disable -Wformat in that config for now.

Bug:  746303 , 746505 , 747638 , 747643 , 724204 

Change-Id: I6196a2a173a1b4871f22d0ce92436d0197fd7845
Reviewed-on: https://chromium-review.googlesource.com/582074
Reviewed-by: Hans Wennborg <hans@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#488946}
[modify] https://crrev.com/1c688af81fcfa4c072dcca79e698641839e8a42f/build/config/c++/BUILD.gn
[modify] https://crrev.com/1c688af81fcfa4c072dcca79e698641839e8a42f/build/config/c++/c++.gni
[modify] https://crrev.com/1c688af81fcfa4c072dcca79e698641839e8a42f/build/config/fuchsia/BUILD.gn
[modify] https://crrev.com/1c688af81fcfa4c072dcca79e698641839e8a42f/build/toolchain/toolchain.gni
[modify] https://crrev.com/1c688af81fcfa4c072dcca79e698641839e8a42f/third_party/google_toolbox_for_mac/BUILD.gn
[modify] https://crrev.com/1c688af81fcfa4c072dcca79e698641839e8a42f/tools/clang/scripts/update.py

We rolled in 6.0.0 yesterday and things appear to work.