BUILD: makefile: add entries to build common debugging tools

A few tools in contrib/ such as halog, flags, poll and tcploop are
occasionally useful at least to developers, and some of them such as
halog or flags can occasionally break due to some changes in the include
files. As reported in issue #907, their inability to inherit the global
build options also causes some warnings related to some specificities
of the main include files. Let's just add entries in the main makefile
to build them.
diff --git a/Makefile b/Makefile
index 2fb05c7..85ca45e 100644
--- a/Makefile
+++ b/Makefile
@@ -888,6 +888,18 @@
 %.o:	%.c $(DEP)
 	$(cmd_CC) $(COPTS) -c -o $@ $<
 
+contrib/halog/halog:
+	$(Q)$(MAKE) -C contrib/halog halog CC='$(cmd_CC)' OPTIMIZE='$(COPTS)'
+
+contrib/debug/flags:
+	$(Q)$(MAKE) -C contrib/debug flags CC='$(cmd_CC)' OPTIMIZE='$(COPTS)'
+
+contrib/debug/poll:
+	$(Q)$(MAKE) -C contrib/debug poll CC='$(cmd_CC)' OPTIMIZE='$(COPTS)'
+
+contrib/tcploop/tcploop:
+	$(Q)$(MAKE) -C contrib/tcploop tcploop CC='$(cmd_CC)' OPTIMIZE='$(COPTS)'
+
 # rebuild it every time
 .PHONY: src/version.c
 
@@ -943,6 +955,7 @@
 	$(Q)for dir in . src include/* doc; do rm -f $$dir/*~ $$dir/*.rej $$dir/core; done
 	$(Q)rm -f haproxy-$(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/halog/halog contrib/debug/flags contrib/debug/poll contrib/tcploop/tcploop
 
 tags:
 	$(Q)find src include \( -name '*.c' -o -name '*.h' \) -print0 | \