MIPS64: Reland 'Enable shorten-64-to-32 warning.'

MIPS64: Reland 'Enable shorten-64-to-32 warning.'

Port cdc43bc5fd02fff2905e2e28a79054d0d1eee3ea

Original review: https://codereview.chromium.org/1133163005/

Original commit message:
Enable clang's shorten-64-to-32 warning flag on ARM64, and fix the warnings
that arise.

BUG=

Committed: https://crrev.com/a12f11911255806d76c016d8332b9b950759c4f9
Cr-Commit-Position: refs/heads/master@{#29024}

[balazs.kilvady, 2015-06-15 11:17:33]

balazs.kilvady@imgtec.com changed reviewers:
+ akos.palfi@mattakis.com, danno@chromium.org, dusan.milosavljevic@imgtec.com,
jkummerow@chromium.org, machenbach@chromium.org, martyn.capewell@arm.com,
paul.lind@imgtec.com, svenpanne@chromium.org

[balazs.kilvady, 2015-06-15 11:17:34]

This does need a v8-team review on a standlone.gypi (was LGTMed earlier). We
removed the mac related parts and plan to make a followup CL for mac. PTAL

[Jakob Kummerow, 2015-06-15 11:32:40]

lgtm

[balazs.kilvady, 2015-06-15 11:43:55]

The CQ bit was checked by balazs.kilvady@imgtec.com

[commit-bot: I haz the power, 2015-06-15 11:44:01]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1182193004/1

[commit-bot: I haz the power, 2015-06-15 12:05:13]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-06-15 12:05:28]

Patchset 1 (id:??) landed as
https://crrev.com/a12f11911255806d76c016d8332b9b950759c4f9
Cr-Commit-Position: refs/heads/master@{#29024}