[Bug c++/92900] Cannot use member of packed struct in constexpr

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92900

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Since accessing a misaligned variable is undefined behaviour, I don't think it
should be permitted in constant expressions (at least for the cases where the
alignment is reduced from its natural value).