[flang] [mlir] [libunwind] [lld] [clang-tools-extra] [llvm] [clang] [openmp] [lldb] [compiler-rt] [BranchFolding] Fix missing predecessors of landing-pad (PR #77608)

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HaohaiWen wrote:

> > This keeps CFG as only have one entry which is required by LiveDebugValues
> 
> If we just want to make LiveDebugValues happy, should it better to remove these died BB instead?

This died BB was already removed by BranchFolder. See rebased test diff. We just want to salvage its successors info.

https://github.com/llvm/llvm-project/pull/77608