[Bug libstdc++/60448] swap_ranges does not use ADL correctly

[glisse at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60448

--- Comment #13 from Marc Glisse <glisse at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #10)
> (In reply to Marc Glisse from comment #6)
> > libc++ sfinae constrains std::swap.
> 
> Aha!  I suppose we could do that too,

Indeed. I could never estimate the drawbacks properly. Doesn't it force types
to be complete earlier than it would otherwise? It probably isn't that bad if
libc++ got away with it.