sudo: needs MMU support

Fixes
http://autobuild.buildroot.org/results/46bcd9601233ca14d6747d9219669e4f52f147e6/build-end.log

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/sudo/Config.in

@@ -1,5 +1,7 @@
 config BR2_PACKAGE_SUDO
 	bool "sudo"
+	# uses fork()
+	depends on BR2_USE_MMU
 	help
 	  Sudo is a program designed to allow a sysadmin to give
 	  limited root privileges to users and log root activity.  The