[llvm] [FixIrreducible][UnifyLoopExits] Fix callbr multiedge splitting (PR #207598)

[Robert Imschweiler via llvm-commits]

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@@ -279,6 +279,7 @@ LLVM_ABI BasicBlock *SplitEdge(BasicBlock *From, BasicBlock *To,
 /// \param Succ           original successor block
 /// \param SuccIdx        index of the original successor in the callbr
 ///                       instruction
+/// \param CallBrTarget   optional \p BasicBlock to reuse for the split
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ro-i wrote:

Let's keep it at what you have now

https://github.com/llvm/llvm-project/pull/207598