[Bug c++/92894] "declared using local type 'test01()::X', is used but never defined" during concept satisfaction

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92894

--- Comment #4 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Created attachment 48428
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=48428&action=edit
avoid defining _IMove::operator() with a deduced return type

With this patch both of the above testcases successfully compile, which seems
to suggest that ranges::iter_move's deduced return type is indeed the problem.