[llvm] AtomicExpand: Stop precollecting atomic instructions in function (PR #102914)

[Alexis Engelke via llvm-commits]

aengelke wrote:

FWIW, I planned to merge the pre-isel legalizing passes (expand atomics, large div/rem, large fp, indirectbr, callbr) into one pass to avoid scanning the IR multiple times. From that perspective, I like the refactoring.

https://github.com/llvm/llvm-project/pull/102914