Disable all code motion on the final optimization attempt.

Disable all code motion on the final optimization attempt.

Before, we disabled code motion for check instructions on the final
optimization attempt.  It is unsafe to prevent movement of check
instructions but to allow movement of instructions that assume the checks
were performed.

Committed: http://code.google.com/p/v8/source/detail?r=6485

[fschneider, 2011-01-26 10:24:35]

LGTM.