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

[Aaron Ballman via llvm-commits]

AaronBallman wrote:

> Did this patch undergo Windows CI testing?

I believe so: https://github.com/llvm/llvm-project/actions/runs/16124071447/job/45496681724

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