PPC: [builtins] Make sure argument count is always valid for C++ builtins.

PPC: [builtins] Make sure argument count is always valid for C++ builtins.

Port 9c8262f11e3d6359874a63f25a31c6ddfba3dc1c

Original commit message:
    When calling into C++ builtins, we need to make sure that the argument
    count register contains the correct number of arguments, otherwise the
    CEntryStub will not be able to leave the stack in the correct state.

R=bmeurer@chromium.org, joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com, dstence@us.ibm.com
BUG=v8:4413
LOG=n

Committed: https://crrev.com/3d1d7f3622d81c92df9a574293b9a48e1eee10d3
Cr-Commit-Position: refs/heads/master@{#31126}

[JoranSiu, 2015-10-06 14:47:06]

lgtm

[MTBrandyberry, 2015-10-06 14:51:35]

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

[commit-bot: I haz the power, 2015-10-06 14:51:45]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1388993002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1388993002/1

[commit-bot: I haz the power, 2015-10-06 15:13:23]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-10-06 15:13:51]

Patchset 1 (id:??) landed as
https://crrev.com/3d1d7f3622d81c92df9a574293b9a48e1eee10d3
Cr-Commit-Position: refs/heads/master@{#31126}