[llvm] BPF: Ensure __sync_fetch_and_add() always generate atomic_fetch_add insn (PR #101428)

[Bryce Kahle via llvm-commits]

brycekahle wrote:

@eddyz87 You are still using `clang --target=bpf`, you have to use the default target.

https://github.com/llvm/llvm-project/pull/101428