Revert of Switch CrWinClang to gn again.

Revert of Switch CrWinClang to gn again. (patchset #1 id:1 of https://codereview.chromium.org/2043743003/ )

Reason for revert:
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

Original issue's description:
> 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}

TBR=dpranke@chromium.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=498033
Committed: https://crrev.com/ab4b1d0c4343dae872c6406263f8aa9b7d550f3d
Cr-Commit-Position: refs/heads/master@{#398456}

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

The CQ bit was checked by thakis@chromium.org

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

Created Revert of Switch CrWinClang to gn again.

[commit-bot: I haz the power, 2016-06-08 00:42:01]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/2049583002/1

[Dirk Pranke, 2016-06-08 01:25:15]

lgtm

[commit-bot: I haz the power, 2016-06-08 01:53:48]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-06-08 01:55:15]

Description was changed from

==========
Revert of Switch CrWinClang to gn again. (patchset #1 id:1 of
https://codereview.chromium.org/2043743003/ )

Reason for revert:
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

Original issue's description:
> 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}

TBR=dpranke@chromium.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=498033
==========

to

==========
Revert of Switch CrWinClang to gn again. (patchset #1 id:1 of
https://codereview.chromium.org/2043743003/ )

Reason for revert:
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

Original issue's description:
> 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}

TBR=dpranke@chromium.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=498033

Committed: https://crrev.com/ab4b1d0c4343dae872c6406263f8aa9b7d550f3d
Cr-Commit-Position: refs/heads/master@{#398456}
==========

[commit-bot: I haz the power, 2016-06-08 01:55:16]

Patchset 1 (id:??) landed as
https://crrev.com/ab4b1d0c4343dae872c6406263f8aa9b7d550f3d
Cr-Commit-Position: refs/heads/master@{#398456}

[Nico, 2016-06-21 11:43:42]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.chromium.org/2081973002/ by thakis@chromium.org.

The reason for reverting is: goma bug might be fixed now..