[clang] [llvm] [CodeGen] Fix VNInfo mapping in LiveRange::assign (PR #148790)

[Matt Arsenault via cfe-commits]

================
@@ -257,11 +257,13 @@ namespace llvm {
       assert(Other.segmentSet == nullptr &&
              "Copying of LiveRanges with active SegmentSets is not supported");
       // Duplicate valnos.
+      auto FirstNewVNIIdx = valnos.size();
----------------
arsenm wrote:

```suggestion
      size_t FirstNewVNIIdx = valnos.size();
```
No auto 

https://github.com/llvm/llvm-project/pull/148790