Be more accurate about live range splitting at the end of blocks.

Be more accurate about live range splitting at the end of blocks.

If interference reaches the last split point, it is effectively live out and
should be marked as 'MustSpill'.

This can make a difference when the terminator uses a register. There is no way
that register can be reused in the outgoing CFG bundle, even if it isn't live
out.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@124900 91177308-0d34-0410-b5e6-96231b3b80d8