Use the version of clang shipped with Xcode for official build

Use the version of clang shipped with Xcode for official build

Instead of checking which generator is used to decide whether to use
ToT clang or Xcode clang, make the decision based on the buildtype
instead.

Use the version of clang shipped with Xcode for official build, and
leave the default selected for developer builds (default to ToT clang).

BUG=459148
Committed: https://crrev.com/3ea2d12051d9922ad4834c2efd19adfa1fe71cf1
Cr-Commit-Position: refs/heads/master@{#317627}

[sdefresne, 2015-02-18 10:58:39]

sdefresne@chromium.org changed reviewers:
+ stuartmorgan@chromium.org, thakis@chromium.org

[sdefresne, 2015-02-18 10:58:39]

stuartmorgan: this should give us better warnings on the bots without
introducing changes to the official builder and put us back in the situation we
were in before I started implementing the 64-bit support. Can you take a look?

thakis: as discussed this change the condition to check the buildtype instead of
the generator. I'll also need your OWNERS approval.

[sdefresne, 2015-02-23 10:24:02]

Ping?

[Nico, 2015-02-23 16:55:43]

On 2015/02/23 10:24:02, sdefresne wrote:
> Ping?

Lgtm

I think this is great, but I was waiting for stuart. I guess he was waiting for
me :-P

[stuartmorgan, 2015-02-23 17:48:24]

LGTM. (I'm actually just really behind on reviews, and needed to think through
the implications of this on the whole downstream waterfall.)

Please send a PSA to downstream sheriffs once this lands so that people know to
consider this if they hit cases where only official bots fail to compile.

[sdefresne, 2015-02-23 17:55:29]

The CQ bit was checked by sdefresne@chromium.org

[commit-bot: I haz the power, 2015-02-23 17:56:32]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/936013002/1

[commit-bot: I haz the power, 2015-02-23 19:48:59]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-02-23 19:49:30]

Patchset 1 (id:??) landed as
https://crrev.com/3ea2d12051d9922ad4834c2efd19adfa1fe71cf1
Cr-Commit-Position: refs/heads/master@{#317627}