[Bug c++/89285] [8 Regression] ICE after casting the this pointer in the constructor in C++17 mode

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89285

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
I think it's valid (but the constructor can't be used in a constant
expression).