Rolling forward clang, hiding some warnings

Rolling forward clang, hiding some warnings.

tools/clang/ directory copied from Chromium's master.

build/config/compiler/BUILD.gn edited manually to silence warnings.

R=jamesr@chromium.org, phosek@chromium.org

Committed: https://chromium.googlesource.com/external/mojo/+/4fdc9529bf7f89e80efcca6c44b9aa161d34bdcb

[Sean Klein, 2015-10-20 18:37:49]

Description was changed from

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Rolling forward clang, hiding some warnings
==========

to

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Rolling forward clang, hiding some warnings.

tools/clang/ directory copied from Chromium's master.

build/config/compiler/BUILD.gn edited manually to silence warnings.
==========

[Sean Klein, 2015-10-20 18:40:28]

smklein@chromium.org changed reviewers:
+ phosek@chromium.org

[Sean Klein, 2015-10-20 18:40:28]

I'm unsure if all of these changes are necessary.
This is building with an updated clang (and on my machine, mojob.py build + test
both work).

[Petr Hosek, 2015-10-20 21:13:23]

lgtm

[Sean Klein, 2015-10-20 21:15:49]

smklein@chromium.org changed reviewers:
+ viettrungluu@chromium.org

[viettrungluu, 2015-10-20 21:17:29]

viettrungluu@chromium.org changed reviewers:
+ jamesr@chromium.org

[viettrungluu, 2015-10-20 21:17:29]

+jamesr

[jamesr, 2015-10-20 21:26:50]

lgtm

[Sean Klein, 2015-10-20 21:35:51]

Committed patchset #3 (id:40001) manually as
4fdc9529bf7f89e80efcca6c44b9aa161d34bdcb (presubmit successful).