[llvm] [clang-tools-extra] [clang] Add out-of-line-atomics support to GlobalISel (PR #74588)

[Amara Emerson via cfe-commits]

https://github.com/aemerson commented:

Not an expert on atomics, but why would we have a libcall for -O0 but not for O1 in the tests?

https://github.com/llvm/llvm-project/pull/74588