[Bug libstdc++/83981] vector::resize(size_type) should not require T to be CopyInsertable when std=c++14

[dtrebbien at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83981

--- Comment #7 from Daniel Trebbien <dtrebbien at gmail dot com> ---
So as not to break testsuite/23_containers/vector/capacity/resize/moveable2.cc
for C++11, I decided that it would be best to keep the use of
std::__uninitialized_move_if_noexcept_a() when compiling as C++11. Please see
my proposed patch.