strongswan: needs threads

Fixes:
http://autobuild.buildroot.net/results/e23/e2394705545dad8e33ffc558df518014c15f5271/

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/strongswan/Config.in

@@ -1,6 +1,10 @@
+comment "strongswan needs a toolchain w/ threads"
+	depends on !BR2_TOOLCHAIN_HAS_THREADS
+
 menuconfig BR2_PACKAGE_STRONGSWAN
 	bool "strongswan"
 	depends on BR2_USE_MMU # fork()
+	depends on BR2_TOOLCHAIN_HAS_THREADS
 	help
 	  strongSwan is an OpenSource IPsec implementation for the
 	  Linux operating system. It is based on the discontinued