[llvm] [SPIRV] Preserve implicit bitcast (PR #151041)

[Chris B via llvm-commits]

================
@@ -136,7 +139,9 @@ class SPIRVLegalizePointerCast : public FunctionPass {
                                            OriginalOperand, LI);
     }
     // Destination is a smaller vector than source.
+    // or different vector type.
----------------
llvm-beanz wrote:

```suggestion
    // Destination is a smaller vector than source or different vector type.
```

https://github.com/llvm/llvm-project/pull/151041