[llvm] [MachineSink] Sink into consistent blocks for optsize funcs (PR #115367)

[Steven Johnson via llvm-commits]

steven-johnson wrote:

The new comparator passed to stable-sort doesn't follow a strict-weak ordering, and so when running under Address Sanitizer, we can (and do!) fail at runtime with `Your comparator is not a valid strict-weak ordering` due to ASAN's extra runtime checking; this means that using the JIT with this change is unreliable. This change should be reverted or fixed-forward.

https://github.com/llvm/llvm-project/pull/115367