We do not support splitting cleanuppad or catchswitches. This is
problematic for passes which assume that a loop is in loop simplify
form (the loop would have a dedicated exit block instead of sharing it).
While it isn't great that we don't support this for cleanups, we still
cannot make loop-simplify form an assertable precondition because
indirectbr will also disable these sorts of CFG cleanups.
This fixes PR28132.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@272739 91177308-0d34-0410-b5e6-96231b3b80d8
