Use first position in LAllocator ordering heuristic.

This changes the tiebreaker for LAllocator's ordering heuristic of
live ranges to use the first use position instead of the first hinted
use position. Searching for the first hinted position introduces
unnecessary overhead.

R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/14855010

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@14534 ce2b1a6d-e550-0410-aec6-3dcde31c8c00