selftests/mm: rename COW_EXTRA_LIBS to IOURING_EXTRA_LIBS

selftests/mm: rename COW_EXTRA_LIBS to IOURING_EXTRA_LIBS

The macro and facility can be reused in other tests too.  Make it general.

Link: https://lkml.kernel.org/r/20230417195317.898696-6-peterx@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Mika Penttilä <mpenttil@redhat.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Nadav Amit <nadav.amit@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>