[llvm] Fix build break when building RISCVInstrInfo.cpp with MSVC (PR #110342)

[Luke Lau via llvm-commits]

lukel97 wrote:

Thanks for fixing this. What version of MSVC was this showing up with? This seemed to slip past the windows pre-merge CI: https://buildkite.com/llvm-project/github-pull-requests/builds/103512#0192235b-a71e-4dc7-8b7b-6ba3b185f6ac

https://github.com/llvm/llvm-project/pull/110342