Switch CrWinClang to gn again.

Switch CrWinClang to gn again.

This relands parts of https://codereview.chromium.org/1947183004/
Now that clobber runs as a separate step before runhooks, swarming should work
on gn clobber bots.

BUG=498033
Committed: https://crrev.com/9b6d81f1e5b090fbc9eabc88972d1e6cc4369c94
Cr-Commit-Position: refs/heads/master@{#398148}

[Dirk Pranke, 2016-06-06 21:00:33]

dpranke@chromium.org changed reviewers:
+ dpranke@chromium.org

[Dirk Pranke, 2016-06-06 21:00:33]

lgtm

[Nico, 2016-06-06 21:01:04]

The CQ bit was checked by thakis@chromium.org

[commit-bot: I haz the power, 2016-06-06 21:02:04]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/2043743003/1

[commit-bot: I haz the power, 2016-06-06 22:38:36]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-06-06 22:40:14]

Description was changed from

==========
Switch CrWinClang to gn again.

This relands parts of https://codereview.chromium.org/1947183004/
Now that clobber runs as a separate step before runhooks, swarming should work
on gn clobber bots.

BUG=498033
==========

to

==========
Switch CrWinClang to gn again.

This relands parts of https://codereview.chromium.org/1947183004/
Now that clobber runs as a separate step before runhooks, swarming should work
on gn clobber bots.

BUG=498033

Committed: https://crrev.com/9b6d81f1e5b090fbc9eabc88972d1e6cc4369c94
Cr-Commit-Position: refs/heads/master@{#398148}
==========

[commit-bot: I haz the power, 2016-06-06 22:40:15]

Patchset 1 (id:??) landed as
https://crrev.com/9b6d81f1e5b090fbc9eabc88972d1e6cc4369c94
Cr-Commit-Position: refs/heads/master@{#398148}

[Nico, 2016-06-08 00:40:58]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.chromium.org/2049583002/ by thakis@chromium.org.

The reason for reverting is: goma miscompiles things in optimized clang-cl
builds if -imsvc is used (which the gn build uses but the gyp build doesn't),
see https://crbug.com/618038.