mongrel2: needs threads

mongrel2 uses zeromq that needs threads

Fixes: http://autobuild.buildroot.org/results/93d/93da58453e1ca0cc491170976cfbdeb8bee5c648

Signed-off-by: Gilles Talis <gilles.talis@gmail.com>

package/mongrel2/Config.in

@@ -4,6 +4,7 @@ config BR2_PACKAGE_MONGREL2
 	select BR2_PACKAGE_ZEROMQ
 	depends on BR2_INSTALL_LIBSTDCPP # zeromq
 	depends on BR2_INET_IPV6 # zeromq
+	depends on BR2_TOOLCHAIN_HAS_THREADS # zeromq
 	depends on BR2_LARGEFILE # zeromq -> util-linux
 	depends on BR2_USE_WCHAR # zeromq -> util-linux
 	# {get,make,swap}context functions present in