These builtin functions use stdcall calling convention, but compilers
reference them without stdcall declarations.

Otherwise ucrtbase initialization code crashes with +relay enabled when
compiled with clang as a PE build.
Signed-off-by: Dmitry Timoshkov <dmitry@baikal.ru>
Signed-off-by: Jacek Caban <jacek@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>