[Bug c++/125490] GCC accepts an invalid concept that compares sizeof(T) with nullptr

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125490

--- Comment #1 from Drea Pinski <pinskia at gcc dot gnu.org> ---
clang might be wrong here due to the way concepts work.

GCC turns that concept into false though.

So in summary:
GCC and MSVC both handle it as being diagnostic at instantiation time.
clang and EDG both diagnostic it at definition time.