[llvm] [IfConversion] Preserve debug info when flipping a branch (PR #114614)

[Ellis Hoag via llvm-commits]

ellishg wrote:

I saw this comment in a few places and I figured it would be an easy improvement.
```
DebugLoc dl; // FIXME: this is nowhere
```

https://github.com/llvm/llvm-project/pull/114614