[Bug libstdc++/62259] atomic class doesn't enforce required alignment on powerpc64

[hp at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62259

--- Comment #8 from Hans-Peter Nilsson <hp at gcc dot gnu.org> ---
(In reply to Andrew Macleod from comment #4)
> Yeah... up until now, CRIS was the only port that this was an issue for.

And JFTR, the resolution to this PR doesn't solve the similar issue there. (To
wit, increasing alignment up to *that of an integer of* the natural size which
is not the same as "increasing alignment up to the natural size" which would
work.)

> The original C11 work had an extension  __attribute__(atomic)  which would
> do the same thing the _Atomic keyword does for non C11 compilation, and the
> type in the libstdc++ atomic classes would be given this attribute.

This would work.