CONTRIB: debug: split poll from flags

Now poll is its own project and doesn't share the "flags" Makefile
any more. One of the issues was that it was making references to the
haproxy include path which is not needed here.
diff --git a/Makefile b/Makefile
index 2ff6cd3..fc62b13 100644
--- a/Makefile
+++ b/Makefile
@@ -995,7 +995,7 @@
 	$(Q)rm -f haproxy-$(VERSION).tar.gz haproxy-$(VERSION)$(SUBVERS)$(EXTRAVERSION).tar.gz
 	$(Q)rm -f haproxy-$(VERSION) haproxy-$(VERSION)$(SUBVERS)$(EXTRAVERSION) nohup.out gmon.out
 	$(Q)rm -f contrib/*/*.[oas] contrib/*/*/*.[oas] contrib/*/*/*/*.[oas]
-	$(Q)rm -f contrib/halog/halog contrib/debug/flags contrib/debug/poll contrib/tcploop/tcploop
+	$(Q)rm -f contrib/halog/halog contrib/debug/flags contrib/poll/poll contrib/tcploop/tcploop
 
 tags:
 	$(Q)find src include \( -name '*.c' -o -name '*.h' \) -print0 | \