Clang update script: support fetching pre-built CMake on Mac

Clang update script: support fetching pre-built CMake on Mac

Both cmake310_Linux.tgz and cmake310_Darwin.tgz exist now.
I'll remove the poorly named cmake310.tgz when this has landed.

BUG=452726
Committed: https://crrev.com/687f172673dbe2e02c3f8f926232e144ca6f8644
Cr-Commit-Position: refs/heads/master@{#324372}

[hans, 2015-04-09 00:27:02]

hans@chromium.org changed reviewers:
+ thakis@chromium.org

[hans, 2015-04-09 00:27:02]

Please take a look.

One of the machines is up and running:
http://chromegw/i/chromium.fyi/buildslaves/build99-m1

[hans, 2015-04-09 00:30:24]

On 2015/04/09 00:27:02, hans wrote:
> http://chromegw/i/chromium.fyi/buildslaves/build99-m1
Sorry, http://build.chromium.org/p/chromium.fyi/buildslaves/build99-m1

[Nico, 2015-04-09 01:42:19]

lgtm

[hans, 2015-04-09 01:44:57]

The CQ bit was checked by hans@chromium.org

[commit-bot: I haz the power, 2015-04-09 01:46:43]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1073673002/1

[commit-bot: I haz the power, 2015-04-09 04:32:07]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-09 04:32:53]

Patchset 1 (id:??) landed as
https://crrev.com/687f172673dbe2e02c3f8f926232e144ca6f8644
Cr-Commit-Position: refs/heads/master@{#324372}