[NaCl SDK] Re-land "Added support for NaCl IO to use the IRT Extension API."

[NaCl SDK] Re-land "Added support for NaCl IO to use the IRT Extension API."

This change was initially landed at 3183230a and then
reverted at 8c7a8d9a.

In order to better integrate the IRT Extension API into NaCl IO, the
first implementation mirrors the other kernel_wrap_* files. All the
unit tests should therefore still be valid. Eventually it may be
easier to just have a separate version of kernel_intercept which
utilizes the IRT extension API directly.

Currently the IRT Extension interface is only used for the
new arm glibc toolchain, for which there is no other existing
method of interception.

CQ_EXTRA_TRYBOTS=tryserver.chromium.linux:linux_nacl_sdk;tryserver.chromium.mac:mac_nacl_sdk;tryserver.chromium.win:win_nacl_sdk
BUG= https://code.google.com/p/nativeclient/issues/detail?id=3918
TEST= trybots

Committed: https://crrev.com/f1de4a508142337557ff1751bc83c9f6866f1e1f
Cr-Commit-Position: refs/heads/master@{#339574}

[Sam Clegg, 2015-07-20 21:41:43]

The CQ bit was checked by sbc@chromium.org to run a CQ dry run

[Sam Clegg, 2015-07-20 21:41:49]

sbc@chromium.org changed reviewers:
+ binji@chromium.org

[commit-bot: I haz the power, 2015-07-20 21:41:55]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1245663004/1

[binji, 2015-07-20 22:04:16]

lgtm

[Sam Clegg, 2015-07-20 23:54:15]

The CQ bit was unchecked by sbc@chromium.org

[Sam Clegg, 2015-07-20 23:54:35]

The CQ bit was checked by sbc@chromium.org

[commit-bot: I haz the power, 2015-07-20 23:55:26]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1245663004/1

[commit-bot: I haz the power, 2015-07-21 00:28:55]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-07-21 00:30:21]

Patchset 1 (id:??) landed as
https://crrev.com/f1de4a508142337557ff1751bc83c9f6866f1e1f
Cr-Commit-Position: refs/heads/master@{#339574}