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

[redi at gcc dot gnu.org]

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

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Although I see no harm in changing the library to take those arguments by
value, the testcase is of course invalid.