[Bug libstdc++/71660] [5/6/7 regression] alignment of std::atomic<8 byte primitive type> (long long, double) is wrong on x86

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71660

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #2)
> We might need a front-end attribute so std::atomic can emulate what the C
> front-end does with _Atomic.

I still think this is the only reliable way to solve this. Trying to emulate
target hooks in C++ template metaprogrammes is doomed to fail.