PPC: [runtime] Add %ToString and %_ToString and remove the TO_STRING builtin.

PPC: [runtime] Add %ToString and %_ToString and remove the TO_STRING builtin.

Port 09de997b3504368d40644afa7310b90faff5d09c

Original commit message:
    This adds a new ToString runtime function and a fast-path ToStringStub
    (which is just a simple dispatcher for existing functionality), and also
    implements %_ToName using the ToStringStub.

R=bmeurer@chromium.org, jyan@ca.ibm.com, dstence@us.ibm.com, joransiu@ca.ibm.com
BUG=v8:4307
LOG=n

Committed: https://crrev.com/50916155b52cddd83c1f26834e0e57fe6f02ccd4
Cr-Commit-Position: refs/heads/master@{#30449}

[dstence, 2015-08-28 14:31:23]

lgtm

[MTBrandyberry, 2015-08-28 15:07:35]

The CQ bit was checked by mbrandy@us.ibm.com

[commit-bot: I haz the power, 2015-08-28 15:07:49]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1310493004/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1310493004/1

[commit-bot: I haz the power, 2015-08-28 15:34:13]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-08-28 15:34:43]

Patchset 1 (id:??) landed as
https://crrev.com/50916155b52cddd83c1f26834e0e57fe6f02ccd4
Cr-Commit-Position: refs/heads/master@{#30449}