[llvm] [RFC][BPF] Do atomic_fetch_*() pattern matching with memory ordering (PR #107343)

[Andrii Nakryiko via llvm-commits]

anakryiko wrote:

> Question: should BPF backend report and error if `__ATOMIC_{CONSUME,ACQUIRE,RELEASE,ACQ_REL}` is used?

Why not use the strongest ordering for all those "intermediate" orderings instead of erroring out? Just use `__ATOMIC_SEQ_CST`? If, in the future, BPF has weaker orderings, then we can always downgrade to that (probably with cpu version bump).

https://github.com/llvm/llvm-project/pull/107343