[llvm] AtomicExpand: Allow incrementally legalizing atomicrmw (PR #103371)

[Eli Friedman via llvm-commits]

efriedma-quic wrote:

To be clear, I think this patch is doing the right thing.  As the code notes, we can't stick an fadd inside an ll/sc loop, so we need to expand in two stages... and doing the second stage early is consistent with the rest of the code.

https://github.com/llvm/llvm-project/pull/103371