[llvm] [LoopPeel] change `peelLoop`'s return type from `bool` to `void` (PR #177488)

[Aiden Grossman via llvm-commits]

https://github.com/boomanaiden154 approved this pull request.

LGTM.

It looks like this was left over from the original implementation in b151a641aa8fe3c1bbb2ed78279ede5f1ecc0e7e and never cleaned up. In that commit, the only user of `peelLoop` also just discarded the return type.

https://github.com/llvm/llvm-project/pull/177488