X87: implement MathPow stub for X87.

X87: implement MathPow stub for X87.

  In CL 0fe2fbd173c5e547e021476428001cac6fcdf7a9 the implementation of
  MathPow for all ports are unified and MathPow stub code is invoked.
  So we move the direct runtime function call from full-codegen to MathPow
  stub for X87 platform.

BUG=

Committed: https://crrev.com/5c5c55fb94d5be4195d1fda72ca535dd014c967e
Cr-Commit-Position: refs/heads/master@{#29865}

[chunyang.dai, 2015-07-27 08:55:09]

Patchset #1 (id:1) has been deleted

[chunyang.dai, 2015-07-27 08:55:36]

chunyang.dai@intel.com changed reviewers:
+ weiliang.lin@intel.com

[chunyang.dai, 2015-07-27 08:55:37]

PTAL.

[Weiliang, 2015-07-27 09:40:36]

The CQ bit was checked by weiliang.lin@intel.com

[Weiliang, 2015-07-27 09:40:36]

lgtm

[commit-bot: I haz the power, 2015-07-27 09:40:49]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1258873002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1258873002/20001

[commit-bot: I haz the power, 2015-07-27 10:05:33]

Committed patchset #1 (id:20001)

[commit-bot: I haz the power, 2015-07-27 10:05:50]

Patchset 1 (id:??) landed as
https://crrev.com/5c5c55fb94d5be4195d1fda72ca535dd014c967e
Cr-Commit-Position: refs/heads/master@{#29865}