[llvm] [IndVars] Use context for proving same sign (PR #181093)

[Antonio Frighetto via llvm-commits]

antoniofrighetto wrote:

> Honestly no idea what formatter is complaining about; I double-check that the patch is clang-formatted. What am I missing?

That's fine, previous lines containing undef have been regenerated. The script might as well be adjusted to warn when a new use of undef is introduced.

https://github.com/llvm/llvm-project/pull/181093