libupnpp: fix libupnp detection with static linking

Fixes http://autobuild.buildroot.net/results/566/566e1510f94670d4ff642c7bfa9918c1d9ec583f/

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/libupnpp/libupnpp.mk

@@ -11,4 +11,10 @@ LIBUPNPP_LICENSE_FILES = COPYING
 LIBUPNPP_INSTALL_STAGING = YES
 LIBUPNPP_DEPENDENCIES = expat libcurl libupnp
 
+# configure script fails to link against the dependencies of libupnp
+# causing upnp detection to fail when statically linking
+ifeq ($(BR2_STATIC_LIBS),y)
+LIBUPNPP_CONF_ENV += LIBS='-lthreadutil -lixml -pthread'
+endif
+
 $(eval $(autotools-package))