[Bug middle-end/92059] Crash on tr2::dynamic_bitset::operator=() with optimization

[jharris at simplexinvestments dot com]

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

--- Comment #2 from John Harris <jharris at simplexinvestments dot com> ---
I figured this out.  The assignment operator doesn't have a return statement.
Why that matters, I don't know.  But adding return *this fixes it.