kbuild: handle any failures of the gen_init_cpio or initramfs image to stop the build.

This also shows how to add files to the initramfs build, but is 
commented out.

Patch originally done by Kai.

usr/Makefile

@@ -7,10 +7,28 @@ clean-files := initramfs_data.cpio.gz
 
 LDFLAGS_initramfs_data.o := $(LDFLAGS_BLOB) -r -T
 
-$(obj)/initramfs_data.o: $(src)/initramfs_data.scr $(obj)/initramfs_data.cpio.gz FORCE
+$(obj)/initramfs_data.o: $(src)/initramfs_data.scr \
+			 $(obj)/initramfs_data.cpio.gz FORCE
 	$(call if_changed,ld)
 
-$(obj)/initramfs_data.cpio.gz: $(obj)/gen_init_cpio
-	./$< | gzip -9c > $@
+# initramfs-y are the programs which will be copied into the CPIO
+# archive. Currently, the filenames are hardcoded in gen_init_cpio,
+# but we need the information for the build as well, so it's duplicated
+# here.
 
+# Commented out for now
+# initramfs-y := $(obj)/root/hello
+
+quiet_cmd_cpio = CPIO    $@
+      cmd_cpio = ./$< > $@
+
+$(obj)/initramfs_data.cpio: $(obj)/gen_init_cpio $(initramfs-y) FORCE
+	$(call if_changed,cpio)
+
+targets += $(obj)/initramfs_data.cpio
+
+$(obj)/initramfs_data.cpio.gz: $(obj)/initramfs_data.cpio FORCE
+	$(call if_changed,gzip)
+
+targets += $(obj)/initramfs_data.cpio.gz