[Bug c++/124447] [reflection] Unable to use reflection in the using statement

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124447

--- Comment #9 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Using reflection on anything inside namespace std is supposed to be
unspecified, so that implementations are free to use equivalent techniques,
e.g. defining a new alias vs redeclaring an existing one with a
using-declaration.

I don't think we want to change anything in namespace std just because
reflection allows you to observe implementation details.

I think we might need a clarification to [namespace.std] so that it also
applies to typedefs and all other entities in std. And maybe also to names
outside std that come from C, because programs should be relying on ::int64_t
being defined any particular way.

I think this bug is INVALID.