Add some build assert macros

Stolen from the linux kernel.

Signed-off-by: Jens Axboe <axboe@fb.com>
stat: ensure that the fp fields are 64-bit aligned

Signed-off-by: Jens Axboe <axboe@fb.com>
fio: add alignment check for fp fields

Signed-off-by: Jens Axboe <axboe@fb.com>
Add alignment to thread_options_pack for proper fp alignment

Signed-off-by: Jens Axboe <axboe@fb.com>