Fix alignment of Code::kConstantPoolOffset.

Fix alignment of Code::kConstantPoolOffset.

This is needed for 64bit alignment sensitive platforms (PowerPC)
Exposed bugs with new GC compare and swap changes updating the
field.

Example failing test:
out/ppc64.debug/cctest  test-decls/ExistsInPrototype

BUG=

[andrew_low, 2014-11-18 15:29:11]

With recent GC changes updating this field with compare and swap, we starting
having new failures on PowerPC 64bit as that platform is alignment sensitive.

Tests such as
out/ppc64.debug/cctest  test-decls/ExistsInPrototype
were failing

This small change addresses that.

[andrew_low, 2014-11-21 14:33:22]

andrew_low@ca.ibm.com changed reviewers:
+ svenpanne@chromium.org

[andrew_low, 2014-11-21 14:33:23]

Forgot to add an actual reviewer (doh)

[Sven Panne, 2014-11-24 07:11:33]

svenpanne@chromium.org changed reviewers:
+ rmcilroy@chromium.org, ulan@chromium.org

[Sven Panne, 2014-11-24 07:11:33]

Delegating to our constant pool black belts... ;-)

[rmcilroy, 2014-11-24 09:39:05]

On 2014/11/24 07:11:33, Sven Panne wrote:
> Delegating to our constant pool black belts... ;-)

lgtm, thanks.

[Sven Panne, 2014-11-24 10:02:36]

The CQ bit was checked by svenpanne@chromium.org

[commit-bot: I haz the power, 2014-11-24 10:03:12]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/740443002/20001

[commit-bot: I haz the power, 2014-11-24 10:22:14]

Committed patchset #2 (id:20001)