[llvm] Avoid dbg.value between phi nodes when converting from DbgRecords (PR #83620)

[Daniel Sanders via llvm-commits]

dsandersllvm wrote:

Closing this one since we have the assert instead (https://github.com/llvm/llvm-project/pull/84054). I've also created 
https://github.com/llvm/llvm-project/pull/84595/files for another behaviour difference between getFirstNonPHI() and getFirstNonPHIIt() where the latter cannot currently be safely used on blocks that only contain phi nodes and have no terminator

https://github.com/llvm/llvm-project/pull/83620