[LoopSimplify] Reuse changeToUnreachable

Use existing functionality provided in changeToUnreachable instead of
reinventing it in LoopSimplify.

No functionality change is intended.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@258663 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed