ARM: Implement correct rounding in the lithium codegenerator.

ARM: Implement correct rounding in the lithium codegenerator.

This patch provides testing for values that have a fraction part of 0.5 and uses a different rounding method for them. The original method of VFPTruncating the value with round-to-nearest is not correct because it does not round to the larger number in case of a tie.

BUG=http://code.google.com/p/v8/issues/detail?id=958

Review URL: http://codereview.chromium.org/6840051

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@7627 ce2b1a6d-e550-0410-aec6-3dcde31c8c00