gn: include CR_CLANG_REVISION in defines for clang

gn: include CR_CLANG_REVISION in defines for clang

This matches gyp behaviour.

R=brettw@chromium.org,thakis@chromium.org
BUG=335824
Committed: https://crrev.com/b1204ef04bc88d632d7458ae070af34b62eafe33
Cr-Commit-Position: refs/heads/master@{#294098}

[Nico, 2014-09-09 23:10:18]

lgtm

[scottmg, 2014-09-09 23:11:01]

The CQ bit was checked by scottmg@chromium.org

[commit-bot: I haz the power, 2014-09-09 23:25:22]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/scottmg@chromium.org/558853002/1

[commit-bot: I haz the power, 2014-09-10 00:29:36]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-09-10 00:29:37]

Try jobs failed on following builders:
  chromium_presubmit on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/chromium_presub...)

[scottmg, 2014-09-10 00:31:02]

Apparently you're the one-and-only-.gn owner Brett.

[brettw, 2014-09-10 03:28:32]

I'm the only build/config owner for now.

LGTM

[scottmg, 2014-09-10 03:40:47]

The CQ bit was checked by scottmg@chromium.org

[commit-bot: I haz the power, 2014-09-10 03:42:16]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/scottmg@chromium.org/558853002/1

[commit-bot: I haz the power, 2014-09-10 03:58:35]

Committed patchset #1 (id:1) as c8fa6ca2469215ee7b27d1e43d2d1311bd4d268b

[commit-bot: I haz the power, 2014-09-10 04:07:34]

Patchset 1 (id:??) landed as
https://crrev.com/b1204ef04bc88d632d7458ae070af34b62eafe33
Cr-Commit-Position: refs/heads/master@{#294098}