test/cpp/Makefile.am: add ZLIB_LIBS to LDFLAGS
diff --git a/test/cpp/Makefile.am b/test/cpp/Makefile.am
index b072440..90aa563 100755
--- a/test/cpp/Makefile.am
+++ b/test/cpp/Makefile.am
@@ -99,7 +99,7 @@
 
 AM_CPPFLAGS = $(BOOST_CPPFLAGS) $(LIBEVENT_CPPFLAGS) -I$(top_srcdir)/lib/cpp/src -Igen-cpp
 AM_CXXFLAGS = -Wall -Wextra -pedantic
-AM_LDFLAGS = $(BOOST_LDFLAGS) $(LIBEVENT_LDFLAGS)
+AM_LDFLAGS = $(BOOST_LDFLAGS) $(LIBEVENT_LDFLAGS) $(ZLIB_LIBS)
 
 clean-local:
 	$(RM) -r gen-cpp