[Bug target/80878] -mcx16 (enable 128 bit CAS) on x86_64 seems not to work on 7.1.0

[crc at winterflaw dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80878

--- Comment #15 from crc at winterflaw dot net ---
On 29/03/18 19:23, andysem at mail dot ru wrote:
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80878
> 
> --- Comment #14 from andysem at mail dot ru ---
>> On Intel, all CAS operations always write, even if thr compare failed.
> 
> I understand that. The question is whether this is allowed behavior for
> atd::atomic::load() operation according to the C++ standard.

Apologies.  I replied off the cuff from my phone; I realised afterwards.