[Bug libstdc++/58403] New: __normal_iterator triggers odr-use

[lichray at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58403

            Bug ID: 58403
           Summary: __normal_iterator triggers odr-use
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: lichray at gmail dot com

Some __normal_iterator's operators take `const difference_type&`, which
triggers odr-use of its argument and results in a linker-error.

Both reverse_iterator and move_iterator take `difference_type`, and
libc++ does it for its __wrap_iter as well.  I think this should be
a recommended choice.