test/pollfree: use mmap(2) instead of a manual syscall
test/pollfree: use mmap(2) instead of a manual syscall

A lot of the syzkaller tests aren't really applicable on non-x86,
or just simply assume x86.

Replace the syscall(__NR_mmap, ...) usage with a regular mmap(2) call,
and check for failure. Looks like some of these assume 4k pages as
well, so just bail if we fail mapping.

Fixes: https://github.com/axboe/liburing/issues/532
Signed-off-by: Jens Axboe <cd8c6775e60d6f67a6984377324e5290df3d5358@kernel.dk>

axboe/liburing,axboe/liburing,axboe/liburing