[llvm] [PowerPC] support branch hint for AtomicExpandImpl::expandAtomicCmpXchg (PR #152366)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm requested changes to this pull request.

There is no plus to adding new target API for this. The bar for new target hooks needs to be higher and have a concrete reason why this would be harmful on other targets (which realistically is only unrelated downstream optimization bugs, so even then it should be unconditional)

https://github.com/llvm/llvm-project/pull/152366