In c++11 char16_t is a distinct fundamental type,
but in c11 it is merely a typedef in <uchar.h>.

Explicitly mention char16_t only in c++11 (where it is built-in),
otherwise define WCHAR as unsigned short (without naming char16_t)
and just hope that on C11 this matches u"..."

Remove WINE_UNICODE_CHAR16; it is now the default when supported.
Signed-off-by: Kevin Puetz <PuetzKevinA@JohnDeere.com>
Signed-off-by: Jacek Caban <jacek@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>