BUG/MINOR: contrib/mod_security: fix build on FreeBSD

Fix linker flags settings since 3rd parties libraries are not in
/usr/lib
Plus libfuzzy needs to be added.
undef LIST_HEAD from event2 which conflicts with haproxy's
diff --git a/contrib/modsecurity/Makefile b/contrib/modsecurity/Makefile
index 72956f9..7853397 100644
--- a/contrib/modsecurity/Makefile
+++ b/contrib/modsecurity/Makefile
@@ -26,7 +26,7 @@
 endif
 
 CFLAGS  = -g -Wall -pthread
-LDFLAGS = -lpthread  -levent -levent_pthreads -lcurl -lapr-1 -laprutil-1 -lxml2 -lpcre -lyajl
+LDFLAGS += -lpthread  -levent -levent_pthreads -lcurl -lapr-1 -laprutil-1 -lxml2 -lpcre -lyajl
 INCS += -I../../include -I../../ebtree -I$(MODSEC_INC) -I$(APACHE2_INC) -I$(APR_INC) -I$(LIBXML_INC)
 LIBS =