userfaultfd: selftest: only warn if __NR_userfaultfd is undefined

userfaultfd: selftest: only warn if __NR_userfaultfd is undefined

Orabug: 21685254

If __NR_userfaultfd is not yet defined by the arch, warn but still build
and run the userfaultfd selftest successfully.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
Cc: Shuah Khan <shuahkh@osg.samsung.com>
Cc: Thierry Reding <treding@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
(cherry picked from commit 56ed8f169e225dce1f9e40f6eee2e2dabe7d06fc)
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Reviewed-by: Dhaval Giani <dhaval.giani@oracle.com>
Signed-off-by: Dhaval Giani <dhaval.giani@oracle.com>