[Bug libstdc++/92059] Crash on tr2::dynamic_bitset::operator=() with optimization

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92059

--- Comment #7 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Yes, I was just looking at that. I think the code predates the rule that a
user-provided move constructor suppresses the implicit copy constructor.