wiringpi: needs threads

Fixes [1]:

  wiringPi.c:66:21: fatal error: pthread.h: No such file or directory

[1] http://autobuild.buildroot.net/results/4e1/4e17697c1116b418d8d9c07a202f3c89186e463f

Signed-off-by: Peter Seiderer <ps.report@gmx.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/wiringpi/Config.in

@@ -1,7 +1,12 @@
 config BR2_PACKAGE_WIRINGPI
 	bool "wiringpi"
 	depends on BR2_USE_MMU # fork()
+	depends on BR2_TOOLCHAIN_HAS_THREADS
 	help
 	  wiringPi libraries (and gpio command)
 
 	  http://wiringpi.com/
+
+comment "wiringpi needs a toolchain w/ threads"
+	depends on BR2_USE_MMU
+	depends on !BR2_TOOLCHAIN_HAS_THREADS