fix type error (arch-dependent) in new aio code
fix type error (arch-dependent) in new aio code

a_store is only valid for int, but ssize_t may be defined as long or
another type. since there is no valid way for another thread to acess
the return value without first checking the error/completion status of
the aiocb anyway, an atomic store is not necessary.

chardi/musl,chardi/musl,chardi/musl