Build 64-bit binaries by default when compiling for iOS

Build 64-bit binaries by default when compiling for iOS

All the bots force the value of target_subarch so the default value is only
used by developpers. Since the vast majority of the devices used on a daily
basis by developpers are 64-bit devices swap the default to 64-bit.

BUG=None

Committed: https://crrev.com/4ef3ab4e104014a35ac36903368b0111c52a1389
Cr-Commit-Position: refs/heads/master@{#323039}

[sdefresne, 2015-03-18 14:57:19]

sdefresne@chromium.org changed reviewers:
+ justincohen@chromium.org, pinkerton@chromium.org

[sdefresne, 2015-03-18 14:57:29]

Let's see if this breaks anything!

[justincohen, 2015-03-18 14:58:17]

LGTM, but confirm with rohitrao/stuargmorgan

[sdefresne, 2015-03-18 15:02:06]

sdefresne@chromium.org changed reviewers:
+ rohitrao@chromium.org

[sdefresne, 2015-03-18 15:04:00]

rohitrao: justin and I both think it would make sense to default to arm64?
compilation time would be unaffected, but launching on 32-bit device/simulator
will cause an error

[rohitrao (ping after 24h), 2015-03-18 15:05:07]

What percentage of our users are on 64bit these days?

[rohitrao (ping after 24h), 2015-03-18 16:18:13]

lgtm

[sdefresne, 2015-03-31 13:40:36]

The CQ bit was checked by sdefresne@chromium.org

[commit-bot: I haz the power, 2015-03-31 13:40:51]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1021513002/1

[commit-bot: I haz the power, 2015-03-31 13:49:46]

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

[commit-bot: I haz the power, 2015-03-31 13:49:47]

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

[sdefresne, 2015-03-31 14:04:00]

sdefresne@chromium.org changed reviewers:
+ jochen@chromium.org

[sdefresne, 2015-03-31 14:04:00]

jochen: OWNERS for build/common.gypi

[jochen (gone - plz use gerrit), 2015-03-31 14:05:44]

lgtm

[sdefresne, 2015-03-31 14:30:32]

The CQ bit was checked by sdefresne@chromium.org

[commit-bot: I haz the power, 2015-03-31 14:30:44]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1021513002/1

[commit-bot: I haz the power, 2015-03-31 15:34:55]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-03-31 15:35:49]

Patchset 1 (id:??) landed as
https://crrev.com/4ef3ab4e104014a35ac36903368b0111c52a1389
Cr-Commit-Position: refs/heads/master@{#323039}