[Bug c++/96645] [9/10/11/12 Regression] [CWG2335] std::variant default constructor and unparsed DMI

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96645

--- Comment #15 from Jason Merrill <jason at gcc dot gnu.org> ---
Created attachment 52663
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=52663&action=edit
patch to make dependency on unparsed DMI a hard error

This doesn't seem to break anything in the library, only the two front-end
tests that were specifically for the SFINAE behavior.