PPC: [builtins] Pass correct number of arguments after adapting arguments.

PPC: [builtins] Pass correct number of arguments after adapting arguments.

Port fbad63669e309e8c5c3f2ecf503df2fefaac79bb

Original commit message:
    The call protocol requires that the register dedicated to the number of
    actual arguments (i.e. rax on x64) always contains the actual arguments.
    That means after adapting arguments it should match the number of
    expected arguments.  But currently we pass some semi-random value
    (usually some stack address) after adapting arguments.

    It looks like this is currently not observable anywhere, because our
    builtins and functions either don't look at the number of arguments and
    just make hard coded (unchecked) assumptions, or are marked as "don't
    adapt arguments", which bypasses the broken code in the trampoline for
    arguments adaption.  Nevertheless this should be fixed.

R=bmeurer@chromium.org, jyan@ca.ibm.com, dstence@us.ibm.com, joransiu@ca.ibm.com
BUG=

Committed: https://crrev.com/8b781ecc5df89b083428fb28912c330ed331a79d
Cr-Commit-Position: refs/heads/master@{#30480}

[JoranSiu, 2015-08-31 16:06:01]

lgtm

[MTBrandyberry, 2015-08-31 16:06:26]

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

[commit-bot: I haz the power, 2015-08-31 16:06:37]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1306953005/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1306953005/1

[commit-bot: I haz the power, 2015-08-31 16:32:39]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-08-31 16:33:01]

Patchset 1 (id:??) landed as
https://crrev.com/8b781ecc5df89b083428fb28912c330ed331a79d
Cr-Commit-Position: refs/heads/master@{#30480}