https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97250
--- Comment #5 from Florian Weimer <fw at gcc dot gnu.org> --- (In reply to H.J. Lu from comment #4) > x86-64-v2 includes CMPXCHG16B, aka CX16. But -mcx16 doesn't define __CX16__. It's called __GCC_HAVE_SYNC_COMPARE_AND_SWAP_16, I think. Is this good enough?
