[Bug libstdc++/66146] call_once not C++11-compliant on ppc64le

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66146

--- Comment #17 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Yes, I think we need to do that, because even if glibc were to change that
wouldn't help on non-gnu targets.