[Bug target/105162] [AArch64] outline-atomics drops dmb ish barrier on __sync builtins

[spop at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105162

--- Comment #4 from Sebastian Pop <spop at gcc dot gnu.org> ---
The attached patch degrades performance on cpus with LSE: the barrier is not
needed when outline-atomics execute an LSE instruction.

I was thinking to add the barrier to the armv8.0 generic path (no LSE) in the
outline-atomics functions.