package/iputils: fix build with thread support disabled

Fixes:
http://autobuild.buildroot.net/results/10652b7bf6a606f0dd802916006c44abf3e5e059
http://autobuild.buildroot.net/results/9656af1aafbd2624fb75bf5fc1dfa13b6175c10b
http://autobuild.buildroot.net/results/2e170e149b293d40978e158d55dc0102315b9d86

Signed-off-by: Petr Vorel <petr.vorel@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/iputils/iputils.mk

@@ -49,6 +49,11 @@ IPUTILS_CONF_OPTS += -DUSE_CRYPTO=none
 IPUTILS_CONF_OPTS += -DBUILD_NINFOD=false
 endif
 
+# ninfod requires <pthread.h>
+ifneq ($(BR2_TOOLCHAIN_HAS_THREADS),y)
+IPUTILS_CONF_OPTS += -DBUILD_NINFOD=false
+endif
+
 ifeq ($(BR2_SYSTEM_ENABLE_NLS),y)
 IPUTILS_CONF_OPTS += -DUSE_GETTEXT=true
 else