The header synopsis for defines macros within the scope of namespace std. AFAICT, all other headers consistently define macros outside of any namespaces, to minimize confusion. Most of the <cstd*> headers defer all macros to after namespace std, although <cstdlib> defines macros /near/ the top of the file, closing and re-opening namespace std.

Suggest moving the atomic macro definitions to the top of the file, above the opening of namespace std, and potentially simplifying by moving the macros up there as well.