skeleton: add default login port to /etc/securetty

We ran into a "Login incorrect" problem when running the same rootfs
image across platforms with different loging ports ttyS0/1/2/3.

Simply assignning "console" to BR2_TARGET_GENERIC_GETTY_PORT, which in
turn modifies the /etc/inittab, is not enough because the "console" device
was missing in the /etc/securetty.

While current securetty has enumerated a lot of ttys, this patch should save
some efforts to enumerate more.

[Peter: guard with single quotes]
Signed-off-by: Tzu-Jung Lee <tjlee@ambarella.com>
Signed-off-by: Spenser Gilliland <spenser@gillilanding.com>
Acked-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

support/scripts/graph-depends

@@ -161,6 +161,7 @@ def remove_redundant_deps(deps):
     return newdeps
 
 TARGET_EXCEPTIONS = [
+    "target-generic-securetty",
     "target-generic-issue",
     "target-generic-getty-busybox",
     "target-generic-do-remount-rw",

system/system.mk

@@ -9,6 +9,10 @@ TARGET_GENERIC_GETTY:=$(call qstrip,$(BR2_TARGET_GENERIC_GETTY_PORT))
 TARGET_GENERIC_GETTY_BAUDRATE:=$(call qstrip,$(BR2_TARGET_GENERIC_GETTY_BAUDRATE))
 TARGET_GENERIC_GETTY_TERM:=$(call qstrip,$(BR2_TARGET_GENERIC_GETTY_TERM))
 
+target-generic-securetty:
+	grep -q '^$(TARGET_GENERIC_GETTY)$$' $(TARGET_DIR)/etc/securetty || \
+		echo '$(TARGET_GENERIC_GETTY)' >> $(TARGET_DIR)/etc/securetty
+
 target-generic-hostname:
 	mkdir -p $(TARGET_DIR)/etc
 	echo "$(TARGET_GENERIC_HOSTNAME)" > $(TARGET_DIR)/etc/hostname
@@ -40,6 +44,10 @@ target-generic-do-remount-rw:
 target-generic-dont-remount-rw:
 	$(SED) '/^[^#].*# REMOUNT_ROOTFS_RW$$/s~^~#~' $(TARGET_DIR)/etc/inittab
 
+ifneq ($(TARGET_GENERIC_GETTY),)
+TARGETS += target-generic-securetty
+endif
+
 ifneq ($(TARGET_GENERIC_HOSTNAME),)
 TARGETS += target-generic-hostname
 endif