Linux: Move aio_write, aio_write64 into libc

Both symbols have to be moved at the same time because they
are intertwined for __WORDSIZE == 64.  The treatment of this case
is also changed to match more closely how the other files suppress
the declaration of the *64 identifier.

The symbols were moved using scripts/move-symbol-to-libc.py.

Reviewed-by: Adhemerva Zanella <adhemerval.zanella@linaro.org>