[CallSiteSplitting] fix use after-free

Iterating through predecessors of `TailBB` while removing their
terminators leads to use after-free, because the predecessor list is
changing on each removal.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@326668 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed