[clang] [llvm] [SROA] Vector promote some memsets (PR #133301)

[via llvm-commits]

macurtis-amd wrote:

@arsenm Any recommendations for appeasing the [undef deprecator](https://github.com/llvm/llvm-project/pull/133301#issuecomment-2759145421)?

https://github.com/llvm/llvm-project/pull/133301