[Bug libstdc++/112876] ranges:to: c.end() is unnecessarily assigned by the return value of c.emplace()

[hewillk at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112876

--- Comment #2 from 康桓瑋 <hewillk at gmail dot com> ---
I believe the above is well-formed after LWG 4016. 

In addition, container-appendable requires `c.emplace(c.end(), *it)` to be
well-formed but `auto end = c.end(); c.emplace(end, *it);` may not be.

Sorry for the pedantic.