Add a rule to put test_stub.o in $(OUTPUT) and change the references to
it accordingly. This prevents test_stub.o from being created in the
source directory.
Signed-off-by: NIlya Leoshkevich <iii@linux.ibm.com>
Acked-by: NAndrii Nakryiko <andriin@fb.com>
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>