Turn on -new-live-intervals by default.

This uses a liveness algorithm that does not depend on data from the
LiveVariables analysis, it is the first step towards removing
LiveVariables completely.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@174774 91177308-0d34-0410-b5e6-96231b3b80d8