[turbofan] Move global constant optimization to AstGraphBuilder.

[turbofan] Move global constant optimization to AstGraphBuilder.

Optimizing global constants such as "NaN", "Infinity" and "undefined" is
best performed during graph building. Then the optimization and lowering
passes only need to deal with real loads in case of JSLoadGlobal.

R=mstarzinger@chromium.org
BUG=v8:4470
LOG=n

Committed: https://crrev.com/74ae226b94f8951cf359f382d1817f08391844f7
Cr-Commit-Position: refs/heads/master@{#31135}

[Benedikt Meurer, 2015-10-05 13:17:50]

Hey Michi,

As discussed offline, unify this in the AstGraphBuilder.
Please take a look.

Thanks,
Benedikt

[Benedikt Meurer, 2015-10-07 07:22:09]

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

[commit-bot: I haz the power, 2015-10-07 07:22:15]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1384953002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1384953002/1

[commit-bot: I haz the power, 2015-10-07 07:46:19]

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

[commit-bot: I haz the power, 2015-10-07 07:46:20]

Dry run: This issue passed the CQ dry run.

[Michael Starzinger, 2015-10-07 08:15:05]

LGTM.

[Benedikt Meurer, 2015-10-07 08:16:04]

The CQ bit was checked by bmeurer@chromium.org

[commit-bot: I haz the power, 2015-10-07 08:16:15]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1384953002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1384953002/1

[commit-bot: I haz the power, 2015-10-07 08:19:30]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-10-07 08:19:53]

Patchset 1 (id:??) landed as
https://crrev.com/74ae226b94f8951cf359f382d1817f08391844f7
Cr-Commit-Position: refs/heads/master@{#31135}