[llvm] llvm-reduce: Add values to return reduction (PR #132686)

[John Regehr via llvm-commits]

regehr wrote:

well, this ended up being more complicated than I thought it would-- thank you for tackling it!

this LGTM, my view is that since llvm-reduce isn't on the critical path for mainstream LLVM development it's fine to try out stuff here and fix it later if needed

https://github.com/llvm/llvm-project/pull/132686