Switch extendInBlock() to take a kill slot instead of the last use slot.

Three out of four clients prefer this interface which is consistent with
extendIntervalEndTo() and LiveRangeCalc::extend().

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@139604 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed