[Bug target/70821] x86_64: __atomic_fetch_add/sub() uses XADD rather than DECL in some cases

[dhowells at redhat dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70821

--- Comment #3 from dhowells at redhat dot com <dhowells at redhat dot com> ---
Yes, I'm testing with -Os.