Unsupported instruction: freeze

```llvm
target triple = "spir64-unknown-unknown"

define spir_kernel void @kernel() {
%1 = freeze i32 undef
ret void
}
```

```
InvalidInstruction: Can't translate llvm instruction:
%1 = freeze i32 undef
[Src: ../lib/SPIRV/SPIRVWriter.cpp:1702 ]
```

Start with the reproducing LLVM IR snippet and the failure reported at lib/SPIRV/SPIRVWriter.cpp:1702. Trace how the translator handles the freeze instruction and compare that path with nearby instruction handling. Done means the snippet no longer raises InvalidInstruction and translates successfully.

Written by the indexing model from the issue text.