* Convert to use LiveVariable analysis

* Convert to use PHIElimination pass
* Don't spill values which have just been reloaded (big win reducing spills)
* Add experimental support for eliminating spills before TwoAddress
  instructions.  It currently is broken so it is #ifdef'd out.
* Use new "is terminator" flag on instructions instead of looking for
  branches and returns explicitly.

llvm-svn: 5219