add randconfig target

Makefile

@@ -332,7 +332,7 @@ config: Kconfig
 	${QUIET}kconfig-qconf Kconfig
 
 randconfig: Kconfig
-	${QUIET}kconfig-conf --randconfig Kconfig
+	${QUIET}script/randconfig
 
 clean: arch_clean
 	rm -f build/system.elf

script/randconfig

+#!/bin/sh
+
+# randconfig occasionally generates invalid configs which lack an application.
+# Try generating a valid config up to ten times.
+
+for i in $(seq 1 10); do
+	kconfig-conf --randconfig Kconfig
+	if grep -F -q CONFIG_app= .config; then
+		exit 0
+	fi
+done
+
+exit 1