[Bug c++/59759] internal compiler error: in unify, using std::enable_if on classes

[trippels at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59759

--- Comment #9 from Markus Trippelsdorf <trippels at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #8)
> If this isn't a regression (which it doesn't seem to be) then setting Target
> Milestone to 4.8.4 doesn't seem appropriate.

Feel free to adjust.