[Bug libstdc++/70893] codecvt incorrectly decodes UTF-16

[kirillnow at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70893

--- Comment #2 from Кирилл <kirillnow at gmail dot com> ---
...
Just realized its wrong endianness problem. 
codecvt_utf8_utf16 should assume utf16be by default, right? Apparently, no.