Update UnrollRuntimeLoopRemainder to always give priority to the UnrollRuntimeMultiExit option, if provided. After ad9da92cf6f7357 (https://github.com/llvm/llvm-project/pull/124462), we would ignore the option if the backend indicates multi-exit is profitable. This means it cannot be used to disable runtime unrolling. To be consistent with canProfitablyRuntimeUnrollMultiExitLoop, always respect the option. This surfaced while discussing https://github.com/llvm/llvm-project/pull/131998. PR: https://github.com/llvm/llvm-project/pull/134259