not very useful without tools, and the contrib Makefile has a gnu-ism

Index: Makefile.in
--- Makefile.in.orig
+++ Makefile.in
@@ -459,7 +459,7 @@ top_srcdir = @top_srcdir@
 # OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 # WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 SUBDIRS = lib tests third-party src bpf examples integration-tests \
-	doc contrib
+	doc
 
 ACLOCAL_AMFLAGS = -I m4
 dist_doc_DATA = README.rst
