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

[pinskia at gcc dot gnu.org]

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

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Depends on|                            |91719

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
PR 91719 says this was fixed in GCC 10.1.0


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91719
[Bug 91719] gcc compiles seq_cst store on x86-64 differently from clang/icc