[Bug libstdc++/60940] general operations on atomic types do not work with atomic integral typedefs

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60940

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Additionally, we fail to meet this requirement:

29.6.2  Templated operations on atomic types  [atomics.types.operations.templ]
The implementation shall declare but not define the function templates
identified as “templated operations on atomic types” in 29.2.

We only declare those functions templates when they need to be defined, i.e.
for arguments of type __atomic_base or atomic<T*>.

The declarations would need to be constrained with SFINAE to prevent them being
used for types derived from __atomic_base.