PPC: [turbofan] Fix tail call optimization.

PPC: [turbofan] Fix tail call optimization.

Port d21de2a48bc63823876d3f9bf52753f9da0aea6b

Original commit message:
Tail calls are matched on the graph, with a dedicated tail call
optimization that is actually testable. The instruction selection can
still fall back to a regular if the platform constraints don't allow to
emit a tail call (i.e. the return locations of caller and callee differ
or the callee takes non-register parameters, which is a restriction that
will be removed in the future).

Also explicitly limit tail call optimization to stubs for now and drop
the global flag.

R=dstence@us.ibm.com, michael_dawson@ca.ibm.com
BUG=

Committed: https://crrev.com/38f7ccba791ea11b10df1c5dfa79bb52c1c441f3
Cr-Commit-Position: refs/heads/master@{#28239}

[dstence, 2015-05-05 17:32:51]

lgtm

[MTBrandyberry, 2015-05-05 17:35:02]

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

[commit-bot: I haz the power, 2015-05-05 17:35:26]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1114193003/1

[commit-bot: I haz the power, 2015-05-05 18:07:16]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-05-05 18:07:32]

Patchset 1 (id:??) landed as
https://crrev.com/38f7ccba791ea11b10df1c5dfa79bb52c1c441f3
Cr-Commit-Position: refs/heads/master@{#28239}