package/haproxy: set USE_DL if needed

haproxy uses dladdr since version 2.2.0 and
http://git.haproxy.org/?p=haproxy.git;a=commit;h=eb8b1ca3eb4c8d4688e1a4a1d9c1b91f68324e09

So set USE_DL to enable linking with -ldl

Fixes:
 - http://autobuild.buildroot.org/results/7bb76153b7dd8f392b247569c53d0f4cbf408371

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/haproxy/haproxy.mk

@@ -15,6 +15,10 @@ HAPROXY_MAKE_OPTS = \
 	PREFIX=/usr \
 	TARGET=custom
 
+ifeq ($(BR2_STATIC_LIBS),)
+HAPROXY_MAKE_OPTS += USE_DL=1
+endif
+
 ifeq ($(BR2_TOOLCHAIN_HAS_LIBATOMIC),y)
 HAPROXY_LIBS += -latomic
 endif