Revert of Reland Make clang the default on linux.

Revert of Reland Make clang the default on linux. (patchset #3 id:40001 of https://codereview.chromium.org/861223002/)

Reason for revert:
Still missing these builders:
http://build.chromium.org/p/client.v8/builders/V8%20Linux%20-%20arm%20-%20sim
http://build.chromium.org/p/client.v8/builders/V8%20Linux%20-%20arm%20-%20sim%20-%20debug
http://build.chromium.org/p/client.v8/builders/V8%20Linux%20-%20full%20debug

Original issue's description:
> Reland Make clang the default on linux.
>
> BUG=
>
> Committed: https://crrev.com/72ef6843b0aff68e519a8f26e7d2f7dd87b4712c
> Cr-Commit-Position: refs/heads/master@{#26204}

TBR=jochen@chromium.org,jkummerow@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=

Committed: https://crrev.com/b0ea0810c6b083857e5f7d647e6d74b6d8d97c37
Cr-Commit-Position: refs/heads/master@{#26205}

[Michael Achenbach, 2015-01-21 20:37:09]

Created Revert of Reland Make clang the default on linux.

[commit-bot: I haz the power, 2015-01-21 20:38:17]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/864093004/1

[commit-bot: I haz the power, 2015-01-21 20:38:30]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-01-21 20:38:44]

Patchset 1 (id:??) landed as
https://crrev.com/b0ea0810c6b083857e5f7d647e6d74b6d8d97c37
Cr-Commit-Position: refs/heads/master@{#26205}

[Michael Achenbach, 2015-01-21 22:11:41]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.chromium.org/862173002/ by machenbach@chromium.org.

The reason for reverting is: Lets try again.