[Bug libstdc++/78805] std::vector::emplace_back is not exception safe.

[lanxingcan at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78805

--- Comment #1 from Xingcan Lan <lanxingcan at gmail dot com> ---
In addition, this bug affects at least from GCC 4.8.x to GCC 6.x, earlier
version of GCC was not yet tested.