[NFC] API for signaling that the current loop is being deleted

We are planning to be able to delete the current loop in LoopSimplifyCFG
in the future. Add API to notify the loop pass manager that it happened.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@354314 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed