patch avoids this issue, by creating a .unpacked file in the squashfs directory
after the source tarball is unpacked, and making the mksquashfs target depend
on the .unpacked file.
http://bugs.busybox.net/view.php?id=234
$(DL_DIR)/$(SQUASHFS_SOURCE):
$(WGET) -P $(DL_DIR) $(SQUASHFS_SITE)/$(SQUASHFS_SOURCE)
-$(SQUASHFS_DIR): $(DL_DIR)/$(SQUASHFS_SOURCE) #$(SQUASHFS_PATCH)
+$(SQUASHFS_DIR)/.unpacked: $(DL_DIR)/$(SQUASHFS_SOURCE) #$(SQUASHFS_PATCH)
zcat $(DL_DIR)/$(SQUASHFS_SOURCE) | tar -C $(BUILD_DIR) -xvf -
toolchain/patch-kernel.sh $(SQUASHFS_DIR) target/squashfs/ squashfs.patch
+ touch $(SQUASHFS_DIR)/.unpacked
-$(SQUASHFS_DIR)/squashfs-tools/mksquashfs: $(SQUASHFS_DIR)
+$(SQUASHFS_DIR)/squashfs-tools/mksquashfs: $(SQUASHFS_DIR)/.unpacked
$(MAKE) -C $(SQUASHFS_DIR)/squashfs-tools;
squashfs: $(SQUASHFS_DIR)/squashfs-tools/mksquashfs