[llvm] Fix MSVC warning in benchmark (PR #147357)

[Daniel Paoliello via llvm-commits]

dpaoliello wrote:

> > Did this patch undergo Windows CI testing?
> 
> I believe so: https://github.com/llvm/llvm-project/actions/runs/16124071447/job/45496681724

Huh, that build is marked as succeeded, but it looks like nothing was actually built?

@klausler What errors are you seeing? I'm guessing that your CI and my local machine have different versions of MSVC. In the meantime please revert the commit and I'll redo it.

https://github.com/llvm/llvm-project/pull/147357