[Bug libstdc++/56019] max_align_t should be in std namespace

[Jobst.Ziebell at mailbox dot tu-dresden.de]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56019

--- Comment #5 from Jobst.Ziebell at mailbox dot tu-dresden.de ---
I would propose adding something like

#ifdef _GCC_MAX_ALIGN_T
...
#endif
around the 'using' declaration.

(Though I really have no idea whatsoever off gcc internals...)