[Bug target/91719] gcc compiles seq_cst store on x86-64 differently from clang/icc

[vekumar at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91719

--- Comment #10 from vekumar at gcc dot gnu.org ---
xchg is faster than mov+mfence on AMD Zen. We can add m_ZNVER1 | m_ZNVER2 to
the tuning.