[Bug target/95750] [x86] Use dummy atomic insn instead of mfence in __atomic_thread_fence(seq_cst)

[ubizjak at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95750

--- Comment #9 from Uroš Bizjak <ubizjak at gmail dot com> ---
(In reply to Jakub Jelinek from comment #8)

> The culprit is the %esp here, that adds the 0x67 prefix to the insn and
> will only work if %rsp is below 4GB.

Ah, indeed... I was in a bit of hurry and didn't notice.