AArch64 enabling out-of-line atomics by default

Hi all,

I am going to enable outline atomics “-moutline-atomics” by default for baseline AArch64 architecture.

This will allow AArch64 generic compiled code to take advantage of LSE instructions when they are available.

You can always disable outline atomics specifying “-mno-outline-atomics” option.

If you have any concerns please reply here or follow up in review: https://reviews.llvm.org/D93585

Best regards,

Pavel